Combining Hardened and Non-Hardened Armor, How does it stack... Options

[Demerzel]

Okay scenerio:
Imagine a Troll with Orthoshin 3, and Titanium Bone lacing, wearing an armored jacket has an armor rating of (13/11) [(1/1) from troll + (3/3) from Orthoshin + (1/1) From titanim bone lacing + (8/6) from armored jacket].

Said troll gains immunity to normal weapons (Spirit pact, or hybrid/good merge with an insect spirit) lets say at force 4 for example. That's effectvely (8/8) of hardened armor.

Question: how does it combine?

Case 1:
Is it effectively (21/19) all hardened. (The non-hardened armor slows down the bullets/blows then the hardened armor shrugs them off).

Case 2:
Armor rating is effectively (21/19) but only 8/8 of hardened so any damage over 8 still must be resisted, but unless it exceeds 21/19 it's stun.

If case 2 is correct does AP Apply to the hardened part so if you have a modified damage of 8p and AP-1 then you get to do stun? Or does the AP get used up passing through the armored jacket, so that an 8p attack with ap -1 bounces off the hardened part...