act 6 molten vault boss

hi,

just try 2/3 time, but idk if bug or not, when lava reach the end i could only put the boss at 40-45% hp .
i know its a dps check , but i really doubt i'm so low on he..

btw i'm lvl65 arc / spark with manatempest and nice weapon +3lvl+70spell..

on other place i run smoth and down rare or other boss without issue ..

anyone have similar issue ?

ps, maybe i'm not highest dps possible and lightning spell suck a bit, but +40% ..when i see other boss or zone, something wrong here

edit:
and i have only 1 lava wave sequence during fight.