Few days ago my capped ranger ran Coal Chamber. Regular ingredients run on Normal, was not trying to set any records. Had some contracts for clerics 19 and 20, but figured that would be a waste of hireling, so got Isadora Ironclaw (cleric 16).
Apparently that's EXACTLY what one needs in Chamber of Coalescence. Look at Isadora's blue bar:
Also at the clickie weapon I happen to have equipped.