mechanics of penetrate weapon bonus

what is the exact mechanic of penetrate?

eg: a 50 armor gives 50% damage reduction . so a 25% penetrate is:
a) 25% of 50% = 12.5% ?
or b) a flat reduction meaning 50% - 25% = 25% ?

"Ignores (%) of armor mitigation", by wording it's probably (b) but it could mean (a) too
though if it's (a) then wording would be something like "reduces armor mitigation by (%)"
but if it's (b) it's practically the same as powerful bonus " (%) Increased Damage"

so is it (a) or (b) ?

The calculation for how armor rating influences damage (and damage mitigation) is in the wiki.

I've used this to engineer scenarios based in a set amount of damage and the pen reduction on armor rating (Option A).

Basically, Penetrate bonus scales with increasing armor rating.

Here's a table showing it in action on a 25% PenArma

Ignores (%) of armour mitigation to me reads firmly as a