Battering Blows

Last whisper item's ignore BONUS armor. In game you can see the percentage that you obtain through this item. The mastery Batterying blows ignores 7% of armor. It does not specify Bonus. Yet in game, the mastery stacks with the Last whisper' precentage. This is confusing. Also, ignoring 7% of armor is terrible. It's not equivalent to it's counterpart mastery in cunning that reduces armor. Your enemy has to have 200 armor, before you essentially reduce just 14 armor. So the Battering Blows is better against high armor in the long run. However I believe it is still terrible overall. As it is rarely even taken for that reason. The magic reduction from battering blows is also equivalent at a measly 7%. Yet it's even less effective then the armor one, because it barely reduces any magic resist... So for clarity, why does the mastery stack with the last whisper'r, and when will it recieve a buff