It doesn't matter. RAW states that the composite armour can be enchanted. Period. Whether it is masterwork or not is irrelevant in this case.
If you want to increase AC, then Adamantine Body or Mithral Body would help. My kobold has an AC of 20, and the guy is a dualcaster. Do you have any details of your build? Maybe I can help?
Well, as I said it's a Warforged Beguiler//Totemist. This gives me d8 HD and 7/10 BAB.
Stats-wise, the current build is at: STR 14, DEX 14, CON 20, INT 18, WIS 9, CHA 8; This is including a +2 boost (to Int) from burning a FP.
Feats include two from levels (1 and 3) and two from flaws: Jaws of Death, Mithral Body, Multiattack, and Obtain Familiar (so I can get Share Soulmeld later on- This build is highly feat-starved, but should prove fun to play.) This gives me AC 17, and I've got decent HP for a d8 HD pc at 37.
Beguiler gives me casting levels, and spells which are mostly useful for out of combat or if Sinfire throws any anti-incarnum nasties at us (and WF gives me something to do even if he throws both anti-incarnum and anti-magic at the same time... hopefully). Plus, the group currently doesn't have any caster, though if I remember correctly the Uber-Half-Elf is supposed to eventually be a sort of Gish.
Beguiler also gives Armored Mage, meaning even though I can cast, I can wear Light Armor without ASF, particularly in my case, the Mithral plating.
Totemist really seems to call out for gestalting with some full BAB and d10 or better HD class, but this group needs some sort of casting, aside from the divine stuff Phaenix provides. I can certainly live without the familiar and share soulmeld (though a class with an animal companion or mount would also benefit from the feat; however, we're covered on ranger from Phaenix, apparently), as it would open up better armor and a feat slot, but once again, that leaves us without any arcane spellcasting in this team, however limited it is already.