QUOTE(Coma @ May 13 2012, 17:39)

I am pretty sure PA still affect void, as I have eth rapier. After casting Heartseeker, without PA, I do between 1500 and 2600 damage; with PA, I do between 1600 and 3300 damage (for entire Arena session). I think the reason people claim PA cant affect void damage is because they mistake the larger range as the regular non-PA. It is difficult to tell whether PA have effect when I dont know the damage multiplier range (I think it is between 0.5 and 1.5)
Though I dont know about Imperil or whether it will stack with PA.
Let me it out for you simply in math
Imperil does the following 1-(.75)(1-(1-Either Mitigation))
PA does the following 1-0*(1-(1-Physical Mitigation))
So if they had 25% mitigation. (1-(1-(1-.25)))=75% damage taken
with imperil: (1-.75*(1-(1-.25)))=81.25% damage taken
with PA: (1-0*(1-(1-.25)))=100% damage taken
with both: (1-(1-1)*(1-.25)*(1-(1-.25)))=100% damage taken
So PA and Imperil do not stack on MELEE
PA does not affect magical mitigation (didn't before, why would it now)
PA does not affect specific mitigation
Imperil does not affect specific mitigation relating to physical AKA slashing/crushing/piercing (going of the wording)
Imperil does affect elemental mitigation ie. Ice
Imperil double dips on magic by doing the following both decreasing mitigation by 25%, and reducing specific mitigation by 25. (and no, the percent sign was not omitted on accident)
Now assuming 25% mitigation, and 50% elemental mitigation
No spell: (1-(1-(1-.25)))*(1-.5)=37.5% damage taken
with Imperil: (1-0.75*(1-(1-.25)))*(1-.5+.25)=60.9375%
or another possibility: (1-0.75*(1-(1-.25)*(1-.5+.25)))=67.1875%
(not sure which of these two is right yet, haven't gone and tested imperil.
But this is why PA does not stack with imperil and PA still affects void