All skills/feats/enhancements that reduce enemy fortification:
10% reduction Rogue Opportunist,
25% reduction Precision,
10% reduction Improved Sunder,
8% reduction Improved Destruction,
15% reduction Grim Precision (Shadow Dancer)
10% Reduction Piercing Clarity (Grandmaster)
(Edit)Additional Sources:
So, my question would be which of these stack. I have found some threads on the discussing these and trying to mathematically prove if they do, but I'm just looking for player thoughts.
If you were running all of these things, would you really bypass 78% of the targets fortification?
Did I miss anything that could make that percentage higher?