bone break and MERC's decrep

The moment the Pi monsters appear at your vicinity, i assume this will happen:

I assume BB breaks PI, sets it at 99%, then your merc with reapers decrep it, reduces to 49%, assuming it works at full strength…

Someone correct me if im wrong

Decrepify and Amplify Damage work at 100% of their potential against sundered enemies unlike Lower Resist, Conviction, and now Cold Mastery. Bone Break, and sunder charms in general, don't apply to your merc.

Previously immune, now decrepified, enemies you will encounter with sunder on will have 45% phys resist (-5% phys resist, if amplified instead) to your attack.

Interesting question though: How much physical damage will deal your mercenary? He doesn't see the decrepified enemy as sundered. I'd assume they will see them with their previous phy res - 10% (or -20% for amplify, resp.) as the decrep will be applied at 1/5 effectivenes from their point of view.