OK checking my resistance charts (which may not be fully updated but should at least be close) fire shield, and therefore StatusEffectShieldOfFire but also StatusEffectProtectionFire, seems inadequate. It gives only 10 points of fire resistance. Given the current formula, that moves me for example from 42.7% to 43.2% at the next level, and sometimes resistance % still decreases at the next level! (we have to remember that a level up for the player usually means he's gone up even more levels in terms of monsters). In order to maintain roughly the same level of resistance, I'd have to keep investing just in fire shield!
Seems like it needs some tweaking.