Yesterday I experimented a bit with ppu against WBs.
That is only for PvE, not sure if PvP-Calculations are different:
What is even worse than pierce is fire and poison damage.
NC damage reduction is calculated: shields % + armour % + resist skill %
Well if the logs don't lie.
On PA and Blessed Spirit Armour there are no fire and poison resists at all.
I didn't use any resist buffs, only shields and no skill points invested in resists. (You get some force from bones as it counts as skill)
PPU 206 FCS 95
This is with all three shields on:
Against energy you reach the resist cap, due to big amount of resists on armour.
Force resists are second best, then xray.
Fire was the worst, as expected due to no armour resists.
For pierce I would expect the same amount as force because the are equally distributed.
To compensate an armour resist hole you need a lot of skill points invested.
Armour points give more resists per point than skill points.
But this is only true, if the logs don't lie.
I question the logs a bit, because there seems no indication if your armour is "gone" as shown in the UI if you take damage to a body part, and WBs do mostly headshots (+20% damage).
Maybe it is only a PvE thing if your armour is blown away and it makes no difference, or the mechanic is no longer present or the logs lie.