Rending and Penetration interaction

It seems that Rending nerfs weapons with high penetration. It does this due to converting a portion of damage from armor damage to pure damage.

If a weapon has a high penetration and would deal increased increased damage to armored targets, it now deals less damage.

For example, if a weapon deals 110% damage to flak armored targets, but half of that damage is rending, then it would end up doing 105% damage (55% from the half damaging armor, 50% from the half dealing pure damage due to rending).

My proposal for changing rending is to instead influence a slightly different system than weapon damage. All enemies have different percentage damage based on where you hit them and whether that place is armored. I propose rending to decrease the armor effectiveness of an enemy rather than influencing damage.