So, I did a search and haven't found anything...
Fighters get Armor Training that reduces the check penalty and increases the MAX DEX, plus they can move faster in heavier armor. No mention if they are also a spellcaster, does their spell failure get any better? I would assume not (RaW) because it doesn't say so, but why not? Is there errata somewhere that says they do? To me, it would make sense, so I had to ask. If not, we'll probably end up house ruling something. Maybe each level of armor training shaves of 5%... 10%?
Unfortunately, they don't. If you want to move around clad in good armor you need either:
or
Makes you wonder exactly what kind of movement is involved in Arcane spellcasting.
Feels like it ought to, but technically no. Guess it's a rare instance that it comes up as relevant.
5% would be reasonable if you're house ruling; That's -5% at 3rd, -10% at 7th, -15% at 11th and -20% at 15th. Or combining with Arcane Armour Training, 0% for any light armour at 7th, 0% for the ideal breastplate at 11th and a mere 5% with full plate at 15th. Or if you're investing feats for arcane armour mastery, you're done at 11th.
Probably don't want to make it 10% or it makes it very... exploitable, particularly with mithral. If you're doing your few levels in fighter for eldritch knight, I know I'd be kind of tempted to pick up a sash of the war champion and wear a mithral breastplate with no ACP (or maybe even grab arcane armour training and go for the mithral full plate).
Cool. That's what I figured. 5% does sound more reasonable. My group will discuss it in a couple of weeks when we meet again.
Thanks for the help!
Makes you wonder exactly what kind of movement is involved in Arcane spellcasting.
From personal experience driving while wearing full plate armor, even masterfully made armor that covers a person’s arms can make things difficult with quick movements that need to be close to the wearers body. Now why a chain shirt or just a breastplate cause the problem I can’t say.