Oh Yeah, forgot body score as additional soak Dice.
yeah the body armor would end up munching all the AP.
Attacker hits with 12P -4ap attack.
First he soaks with armor jacket rating 10: 10-4ap=soak of 6. He nets two soak successes on average reducing the damage from 12 to 10p.
If the attack is mundane then continue against his itnw power conferred armor:
itnw armor of 10 up against that 10P damage code.
He get 5 auto successes reducing it to 5p damage.
His armor of 10 nets 3 successes on average reducing the damage code to 2p.
Hhmm in your example what would happen if the mundane armour managed to soak 1 more dmg, thus dropping the remaining dmg below the ItNW armour value. Technically it would be immune to the remaining dmg.
I Think I would prefer the hardened armour to be affected first by the AP, thus lessening its power somewhat. (Though, Of course that would mean that Drakes are less powerful as well).
So the spirit would have an armour value of 20. (10 of those are hardened and 10 are normal). Any AP is applied to the hardened armour first.
If the dmg value is lower than the modified armour value, but equal to or higher than the modified hardened armour, then the damage is stun.
If the dmg is lower than the modified hardened armour, then No damage is dealt.