You're falling into a mind set that a lot of people do with magic in this game. That the mundane can't impact the magical.
Remember a maneuver does not have to directly interact with the magic to make it more effective. How loose you can play this depends on the GM, but it's possible.
Example: Vinilla Mortal lobs a flashbang gernade to create the aspect "blind and disoriented" on the enemy. A GM may then allow the wizard creating a zone wide armor evocation to tag that aspect when casting. The rationalization? The enemy is having a much harder time landing direct hits to the point where they aren't as lethal, and allow this to be represented as additional armor bonus on the spell.
Remember, armor and stress is more abstract than it is literal.
Right. because that's just another Flashbang affect. There is a set of rules for that. Aspects are the catch all for the game. They work wonders. Abstracting other game mechanics like that... It messes with the players. Armor is something that physically slows the bullets.
And it isn't anything to do with the system. It has a whole lot to do with the gameworld where Magic is pretty much affected by magic on the positive side of things. There are a multitude of ways to weaken it. But few to strengthen it that a mortal can handle.
Off the top of my head the closest things seen have been the times Harry pulled energy from one place to another. I can see someone starting a car and the wizard yanking the internal combustion energy to power a spell. But I can't say that's a manuever. Possibly an application of the drive skill to keep it going while so much energy is being drained.
Your flashbang thing is an aspect giving a free tag to dodge. How does one use a spell to enhance that effect? More light and sound sure. But making that armor is silly and unnecessary.
The water to stop fire is an aspect allowing tags against the attack. Not armor. It can give the aspect wet which can be tagged to boost water spells. But the water was already there(nearby) in all reality and so could be tagged without the action to unleash it.
Now, i've got you stretching pretty far on that one, which makes my point well enough. It's all very very situational. The characters are more likely to be by a layline.
Now, a thing I noticed while looking through the fatecore stuff.
None of the magic systems appear to cause mental stress. Thoughts? It reinforces my thought that the refresh costs of evocation powers in DFRPG are higher than they would be in Fatecore. However I also don't see weapon values so I could be wrong. But I think it might be interesting that using the powers at 0 weapon value might be a zero stress action then. SO for instance dodging with Discipline via a quickly raised shield that deflects the bullet for 0 stress.
