are you guys still using max mp set for your wraith's hp? or just go in with resist set and summon wraiths with it?
Once you get Death Cry wraith Hp becomes mostly Irrelevant. When Bone Knight is tanking, you're naturally fighting him for aggro. You'll have to resummon pretty frequently to manage hate, and switching between Mp and your main set every 5 sec becomes tedious.
Just keep resummoning him, it's overall better. Only attacks that actually dent him quickly are Rate attack, and Rate attacks would do just as much Hp% dmg to him with 2m Hp compared to 800k.