The way I did it was to first clear the mobs completely from the right side. It's only a few acolytes, the Knight major with the void rifle, the two swords, and a few thrall. I cleared them out first and had a clear shot on Ir with my ghorn without having to deal with the billion adds on the other side. Every time I tried your way, I was free and clear from the melee adds, but got destroyed by everything with a ranged attack. That and Ir kept hiding from me behind the crystal. The flanked attack worked best for me, but I did it by myself. It may be easier your way with more people.