The problem with this line of thinking is that you are separating Evocation blocks with Evocation.  If we are discussing making Evocation blocks more powerful we are discussing making Evocation more powerful.

Everybody already has their own defense rolls based on Athletics or enchanted items.  Evocation block is a boost for Wizards to keep them alive and add on maneuvers.

Most of what we are debating is that Blocks don't work the way Harry uses them.

Nope, they are MUCH more powerful in this system.  Harry's are usually faced in one direction, he couldn't cast while one was up, he could barely act while one was up, and (before a certain point) they could only guard against kenetic.  All things considered, he didn't use his shield bracelet that much.  He usually dodged.

Yup. Speaking of grendelkin, in one of my games, we had a small party fighting one, who had ghouls as its door wardens. While the fighters were in melee, the wizard's main contribution to the fight was to put up and maintain a block on the doorway keeping the Ghouls out long enough for them to bunch up in the hallway...where she could then roast them all wholesale.

Clever.  That's something I had yet to think of... a block used to round things up to be fried.  It's amazing what some of the players have come up with so far.  One character used earth magic to push a warehouse wall down (the building was already damaged), concentrating on tipping it instead of trying to hit the blocking warlock hiding behind it.  He then was subtle enough to use earth magic to soften the mortar on a brick wall for an instant, quiet, breaking and entering.

Back to the topic at hand... I'm trying to think of a way to put a cool supernatural twist on the classic dogfight. Any thoughts?

I don't know much about Warhammer 40k but I was told that Orc vehicles work because they BELIEVE it will work.  What about Fae (or something else from the Nevernever) that created planes somehow mashed together randomly but happen to be able to fly?

The big problem will be the wizard in the group.  You could always choose to not compel his aspect much, or you can counter the thought with an indebted gremlin.  WWII pilots used to talk a lot about gremlins interfering with things.  What if one is caught or bound or a trade is made and these gremlins happen to be able to keep the plan up when they want?

I really don't see how they're underpowered. Really, few antagonists that aren't named major NPCs should be attacking from more than 3, so a 4-shift block on its own is pretty effective against most things. If a caster is equipped properly, they should be able to pull off 8-10 shift shields fairly easily.

I agree, they are absolutely NOT underpowered.  Many wizards will have a 4 or 5 in Conviction.  Many also have a shield bracelet (or an equivalent) that would give a +1.  Finally, many wizards spent an enchanted item slot for something like Harry's Duster.  Now let me show you how this would play out...

Harry enters a room to find there are guys with guns.  He instantly puts up his bracelet with a 6 Power (5 for strength, 1 for 1 extra exchange).  Until his next turn, every enemy has to get a 5 to hit him.  Keep in mind that 5 is something that is so good, many campaigns don't allow a skill that high.  A thug would have maybe a 2 or 3 at guns.  A trained cop would probably have a 4.  Only the best would have higher.  All this is for one mental stress.  Even if one gets through, you can use your duster as armor.  Your block would cancel out most of the attack, and most weapons are 2 or 3, so the duster would stop most or all of it.

Before I continue, compare having to roll Athletics.  Yes, you might get an awesome roll but you are just as likely to get a -2 as you are +2 and how screwed would you be?

Next turn you decide to spend one more casting action to up the duration.  Because you have the shield bracelet you can get it for 6 more exchanges.  Now you've taken your second stress.  (If you had spend an additional stress to make it even higher in the beginning, it would be nearly indestructible.)

Now you have the freedom to move as you please.  You can even turn it into an Armor of 2 if you think your block might get canceled (though it then won't stack with your duster).  With 6 more exchanges, you have options while they poo themselves because their bullets can't hurt you.

Here's the final kicker... you can use that stored shield energy for another spell.  (The rules are on p.260)  As long as there is one exchange left it is never a complete waste.

This isn't even including your ability to protect EVERYBODY.  I think it's one more power required to protect a person next to you or 2 for a zone.  In a group fight, you can put up an area block, saving everybody, then they can attack without fear.  If it counts as armor, they can even dodge while getting your bonus.

The final factor you need to consider is how incredibly overpowered wizards are.  (Which is ok.  I don't mind, my players don't mind)  Evocation gives you this boost to your defense that you wouldn't already have.  It also gives you an incredibly powerful damaging attack.  How many of the other players will have a Weapon Strength: 5 (or higher) attack?  Fine, it costs stress that goes away pretty quickly.  If you have a 5 in Conviction you'll even have an additional mild mental consequence.

If you throw out Evocation like a thug then, yes, it can be underpowered.  Maybe you're facing that creature that is incredibly resistant to magic and is coming towards you to crush everything.  Boost that Fuego up and attack the wooden floor, making the creature fall to the lower floor.  You can't really do that with gun or sword.

Maybe the entire room is filled with vampires.  Heck with it, make it a zone attack and burn EVERYTHING.  Conviction:5 means 5 damage to everybody in the room if they don't get a 6 on their dodge.  (More damage if they get anything less than a 5.)  That only costs ONE STRESS.

Very often I go with narration in my games, and this system is actually designed just for that.

Remember that with spells sometimes you can just choose to add aspects.  (ie if somebody sends out a fire wave, you can just decide there is the aspect Furniture On Fire)

Usually when my players come up with an idea that I think is clever and fun, it pretty much just works.  At worst, I try to make something significant happen so they are encouraged to be creative.  If you bog everything down to die rolls and rules, that's what they will be concerned with.

Also, as a GM you might just say "Maybe for a Fate point you can declare that the bad guy shatters from the sudden change" or something.

This board is invaluable.  I thought this system was really easy when first learning it, but the magic system ended up being a lot more difficult (as magic tends to be).  Thanks everybody!

This is a bit more than you asked for, but bear with me. Fate can do a lot, but sometimes through a lot of different approaches.

I'm glad you did.  Thanks!

For example, you want do a thaumaturgy spell that grants you inhuman strength, and you have a lore of 5. You'll need 5 shifts to take yourself out (less with low endurance), and you need 2 aspects at 3 shifts. That's 11 shifts. 5 of those are covered by your lore of 5. Then you take the hair of an ox, to channel its proverbial strength, which are 2 shifts towards your goal. Since you are pressed for time, you make up the missing 4 shifts by taking the medium consequence of "Torn Muscle Tissue". You'll be all kinds of strong, but your body isn't used to that strength, so it will hurt like hell in the morning.

I read the post you originally linked which led to yet to another which led to a third that talked about Shapeshifting.  Unfortunately, I am still having issues understanding based on some acronyms and other terms I don't understand readily so I have a few questions on this.

1) I've been trying to find out how much stress you need from "Taken Out."  Based on my understanding of concessions needing at least a moderate consequence, my guess is the amount required is the number of stress boxes plus three (to be just barely better than a mild).  Is this correct?

2) I don't understand where you got two aspects at three shifts.  I read the temporary powers rules and can kind of deduce that somehow this is equal to the two fate points needed to be spent for a temporary cost two power, but where does the three come from?  If you could break down your work as if you're talking to a 10-year-old (no offense to you 10-year-olds out there!) I would appreciate it.

I understand the process of trying to reach the complexity, it's DETERMINING the complexity that I'm a little hazy on.

If you only wanted to do a spell that replaces your might skill for one application, that is usually not a problem. A 5 shift effect is most often covered by your lore skill already, there is no need to take consequences to boost the spell. Now if you want to go for a 10 shift replacement spell, that might be another story altogether, and you might be pressed to take that consequence again. Of course, you could use other ingredients (aspects) to boost the spell, instead of consequences. Ground up ants for example, an animal that can carry multiple times it's own weight, could be used in the spell, to offset the negative effects of a strength too big for a human body. In the end, it's all about the story of the spell.

I thought whenever you did enchantments you didn't roll but you simply had a maximum of your Lore plus foci plus specializations, and potions were similar except you could compel aspects upon use to bump them up.  Based on what you said here it seems like you can make enchantments more powerful by taking consequences and spending Fate points upon creation.  Did I misinterpret this?

This is how I see him:
High Concept: Rookie Warden
Trouble: You vampire b***ards killed my mother.
Aspect:  Don't make me angry...
Aspect:   Or diss me.
Aspect:   A European fish in an American pond.
Speaking as guy whose character makes and plays his own instruments, be advised that I went the non-powered route, if you will.  He's popular with folk and jazz players alike.  Regarding Performance, you really don't need more than a 1 or 2 to get an adequate performance. 
Regarding skills, it may be that the reason that he's a rookie and not well-respected is because he's not as skilled as he could/should be.  Maybe his Conviction is high but his Discipline stinks (like many other young punks trying to prove themselves).  Maybe he's too quick to use a weapon or the like, but his skills aren't up to par.  Granted a Warden is a devoted Battle Mage, but perhaps they sent you to an out-of-the-way place both because they wanted you to get more practice and because there aren't that many beasties there to confront.

I like a lot of what BlackStaff said but I would tweak it a bit while adding on some additional thoughts.
"Don't Make Me Angry" and "Or Diss Me" are pretty much the same aspect.  "You Vampire Bs Killed My Mother" can even contain all three if you call it "Vampire Bs Killed My Mother!" which could imply that you are angry in general from being an orphan.

Here's another thought, though.  I don't know how well you know the people in the group you are entering.  When you first start gaming with new people (even if you've met them outside of gaming), you often want to tone down aggression.  Wolverine-tempered characters can be fun, but think of how much Wolverine disturbed the dynamic originally.  You're a young warden, and while you may be hotheaded against enemies you might be a little insecure when it comes to your peers.  Entering a new group you want to have a helpful, team-oriented feel as a first impression.  If you know these people well, feel free to disregard everything I just said in this paragraph.

Why did you leave Europe?  Did you make a huge mistake as a Warden so they are putting you under the tutelage of a Warden in America?  (Just because this other Warden isn't necessarily more powerful doesn't mean they wouldn't think you need to learn from him/her.)  Was something overwhelmingly powerful hunting you over there?  Is the thing that killed your family in the US?  Are you having problems with the mortal society like being accused of a crime you didn't commit?  Did you actually DO the crime you were accused of but the thing you acted against was a bad creature pretending to be human?  (Those mortal laws can be such a nuisance!)

Finally, just because you are from another country and are coming into an existing session doesn't mean that you can't know the characters.  Maybe you were pen-pals with one, or maybe you were visiting right after becoming a warden and helped a player out.  You came to this city for a reason(s).  Each PC can be one of those reasons.  One of my favorite things about this system was smacking into my head how to make the characters already know each other.