Frost Mage AC does not stack

[Flights of Fantasy]

Using one of my characters for build fodder, I've tested out the Frost Mage. I've noticed right away that the Armor of Frost Natural AC bonus does not stack with spells (and probably items). After casting spider skin, I get the usual message about ac bonuses not being able to stack. I'm assuming Armor of Frost is meant to function much like the Dragon Disciple's Dragon Skin.

[Valefort]

Nope, it's not supposed to stack.

[Flights of Fantasy]

From an RP perspective, that doesn't make much sense. Part of the "sacrifice" a character makes in following this path is becoming a creature of the cold, gaining resistance to ice but also becoming weak to fire. Skin becoming ice should warrant a persistent improvement to one's defenses. If it's the amount of AC and a balancing issue, then how about cutting it in half? I'd take +2 Natural AC that's stackable over +4 Natural AC that isn't.

[wangxiuming]

There is an improvement though. The fact that the +4AC doesn't stack with spells and other sources of natural AC doesn't mean it's useless. Rather, it guarantees that a level 10 frostmage will have +4 natural AC regardless of whether he's buffed or whether he's dispelled. He can save a few spell slots in the early levels, and at later levels, he can have the choice of choosing to further increase his AC with spells, or to save that spell slot for other purposes, because he already has +4 natural AC.

There is an improvement to the frostmage's defenses. It's just not as large of an improvement as one that does stack.