yes yes and uh no and yes? idk. But anyways....
ArP will be calculated with a flat percentage from your battle stance. This will NOT be shown in your character Sheet (they should really fix this)
As of now, you have 75.66% reduction including battle stance's 16%.
At this point, I would highly recomend picking up a Banner of Victory from regular 5m ToC, to replace your NES, you should see a dps increase in the static +84 ArP, and the proc is just icing on the cake.