I know I'm in the minority in this, but I use a Defense bonus to AC IMC. I've done so for a little over a year, and nothing bad has happened. Hopefully this'll be helpful =)
Defense
This is a bonus to your armor class based on your level. Your defense bonus represents how adept you are at parrying and blocking melee attacks. You must split your defense bonus against multiple attackers, but you can divide it however you like. (A 14th level fighter with a defense of 9 who’s being attacked by 3 creatures could apply 3 defense to all, 4 points to 2 and 1 point to the other attack, or any combination he chooses, including all his defense on one attacker).
The type of weapon you are (or aren’t) wielding will affect your defense bonus. The modifiers on the accompanying table add together. So if a human fighter is totally unarmed, he gets no defense bonus to his armor class because he loses half his bonus for wielding a tiny weapon, and he also loses half his bonus for being unarmed. A character with the Pugilist (basically Improved Unarmed Strike) feat would only lose half his defense bonus, because while using his fists he counts as armed. A character with the Brawler (next up from IUS) feat wouldn’t lose any bonus because he can use any part of his body as a weapon (and feet are considered small weapons). Armor check penalties apply to your defense bonus, but you can’t have a negative defense bonus from wearing armor.
You don’t get your defense bonus against ranged attacks. You lose your defense bonus whenever you’d lose your Dexterity bonus to AC, excepting certain rare circumstances (such as your feet being glued to the ground, for example).
The Table
Code:
Weapon Effect
Weapon 2+ sizes smaller ½
Unarmed ½
Unproficient weapon ½
Defense increases per level, like saving throws. For example, Fighters have a good Defense (like a good save), rogues have a medium Defense (like a medium save, which isn't in the core books), and wizards have a poor Defense.
, so should not be incorporated in a flat BAB Bonus to AC.
