>>537894029
This is the defense formula. Def ignore/shred applies to DEFtarget here. Basically, since they are multiplicative, the less defense the target has after applying shred/ignore, the less effective pen will be.
For example, if the enemy has the full x1 defense and you have 50% pen ratio, pen makes you ignore 1*0.5=50% of the defense.
If the enemy already has x0.5 defense, pen ratio will make you ignore 0.5*0.5=25% of the defense.