Behold, Southperry. I'm here to help you bust your myths, opinions, and facts or something. Basically this is my attempt at seeing if boss damage truly stacks. I will, however, be needing some assistance on the math, just to see if I'm getting the formulas right.
Kataras and Damage range
Actual Damage Screens
Damage testing gets too tedious, especially with the 1 minute cooldown of Sudden Raid.
Basically speaking, I couldn't test this anymore. Honestly I can't, the one minute cooldown is the biggest pain in the ass known to man. So I couldn't find out if 60% boss damage stacked with 8% total damage, although I'm assuming it does.
Boss damage stacks, and here's mathematical proof and pictures to go with it. Have fun.