Let me preface my comments with, it's your game and you should play however floats your boat. These are just my POV.
As I said in my first post here my problem isn't physics it's fiction, my limiting tactical choices solely to the availability of fate chips you negate the sometimes very interesting story of the tense stand-off where neither party in a conflict can overcome the obstacles between them.
If you can't overcome the obstacles between you, those aren't Aspects. You're not in a conflict. You're safe.
EDIT: Like this...
GM: So, you're pinned down behind this wagon. Their bullets can't reach you, but you know if you break cover you'll expose yourself to danger. What do you do?
You're disincentivising the brilliant tactician or the experienced combatant from having an interesting story roll.
Not sure how. Why would the brilliant tactician prefer camping behind a wagon from brilliantly tacticianing again? The game basically says "If you would like a mechanical advantage in a conflict either 1) do something active or 2) spend a Fate Point (or both). There's tons of room for tactics and brilliance within those parameters.
Finally, and most importantly I think you're pulling the players out of the story by saying that while logically that wagon between you and the other guy would still be relevant here, you're out of this game resource so you're SOL.
Hmm...lets look a that a sec.
GM: Okay, you’re on the street outside the Saloon. I’m placing the aspect “Big sturdy wagon” on the scene, cuz there’s this wagon nearby that could provide cover.
Player: “Wyatt clears leather and opens up on Jesse fanning his gun. Bang, Bang, Bang!” (rolls Weapons).
GM: “Okay Jesse is evading, reaching for his guns (rolls Athletics). Success!”
Player: Miss? I think not. I tag my Angry Ex-Boyfriend aspect. He stole my girl! Get ready for the pain. Take three stress.”
GM: “Looks like I need that cover. He dives behind the wagon and his guns up near his head (Tags the Wagon for a +2).” Then he returns fire, but misses.Okay, I assume we're okay so far. Wyatt fires. He's mad so his Aspect is relevant. Jesse dives behind cover so he can spend Fate on that aspect. But in the next exchange nothing has changed in the fiction. Wyatt is still mad and Jesse is still behind the Wagon. Still, repeatedly playing Wyatt anger rapidly loses interest. But if the game said as long as you roleplay being angry you get your +2 it would incentivize that behavior. Instead the game says it doesn't cost you any more to look around for something else. You pay the same amount of FP, maybe less if you can find a free Tag or if someone can set up one with a Maneuver (hey cooperative play, fancy that!).
It's even more telling with Jesse. He's behind the wagon. In most games there would be a mechanical disincentive for him to break cover and do anything, unless Wyatt's player could negate the cover. Diving for cover is cool. But sitting behind a wagon for multiple rounds is usually boring. Fate says if you want to sit there, pay up. Or, do something else and either pay the same amount or if a free Tag is available maybe make out better. But, you're already incurring the cost, you might as well take action.
But, it’s breaking my mind that the wagon is no longer blocking bullets as effectively, you say? Let’s look at this.
Player: “Okay, that would be a miss, but I’m spending Fate. This dude stole my best girl. I’m pissed. I draw a bead on him (Invokes his “Angry, Ex-Boyfriend” aspect again).”
GM rolls Athletics.
GM: “Not good enough. I’m spending Jesse’s last Fate Point on that Wagon. He hunkers down behind that big ol’ wheel and your bullets are just plunking off of it.”
Player: “I’m invoking my “Deadeye aim” aspect for the win! My bullets find a weak spot in the wagon and rip through the boards.”
How is that any different than if the GM never spent FP on the wagon? It would just be.
Player: “Okay, that would be a miss, but I’m spending Fate. This dude stole my best girl. I’m pissed. I draw a bead on him (Invokes his “Angry, Ex-Boyfriend” aspect again).”
GM “I’m trying not to get shot (rolls Athletics).”
Player: “My bullets find a weak spot in the wagon and rip through the boards.”
In both cases Jesse is behind the wagon and Wyatt’s bullets rip through it. The wagon’s fictional effectiveness at stopping fictional bullets is the same. I’m having a good deal of trouble finding the mind breaking/game distancing part.
Personally I'm in favor of any ruling that allows players for at least a couple of rounds forget that their playing a game but not requiring them to constantly try to work around the resource system.
It's hard for me to respond to that one. Fate doesn't really fade into the background very well, but I see that as a feature. I have never been in a conflict invoking aspects and accepting compels and thought, I wish I could just not engage the system. I'm usually looking for a way to achieve my goals and bring my character's aspects into the fiction. When I am in the mood for a game to do that, I don't reach for DFRPG. Just a YMMV moment, I guess.