Just out of curiosity, why sans Paladin?
I have some issues with shoehorning the fighter into the heavy armor guy role. Why are you specifying heavy armor here? I don't see any balance reason not to let it apply to any worn armor. I don't see any fluff justification for it either. Isn't this supposed to represent an increased skill with using armor to deflect/absorb a blow?-Gain a +1 Armor bonus to AC (stacks with normal armor) while wearing heavy armor at 6th-level and every 6 levels thereafter (12th,18th).