How does these work together?

The former. %Boss is counted under %TotalDamage. They stack additively, i.e. 30% boss with 12% total damage is 42% total damage on bosses.

Here's a writeup, taken from MrTouchNGo's writeup on Shadower DPS.



Except don't use hidden-street to take PDRate values, get them from MapleArchive.