Talk:Armor penetration/@comment-3529242-20121030000306/@comment-4087140-20121030013224

If the target has 100 armor, that would mean they have 200% physical durability (thus, 50% damage reduction). Reducing them to 99 armor results in 199% durability. 200199100.503% damage dealt as a result.

Your statement is essentially correct, though: as enemy armor decreases, flat armor penetration has a more significant effect. Penetrating 20 armor on a 300-armor target isn't anywhere near as useful as penetrating 20 armor on a 30-armor target.