How does the mastery "battering blows" really work? HELP!

In the ferocity tree, lets say you put 5 points in battering blows. Does that +7% armor pen give you bonus armor pen from your runes and items. So say I had 10 armor pen from my rune page, with this mastery would it calculate like this (15 x 0.07 = 1.05) so i then have an additional 1.05 flat armor pen which would be 16.05.

Or does it work in regrades to enemy champions where i penetrate 7% of their armor?

I know how armor pen works but Riot is just so vague in their descriptions on how it is applied. The plus sign (+) is really making it hard to understand what this mastery does.