We have our ranged DPS also running circles, but yes same basic strategy. Melee stack up directly under Kephess while tanks and ranged run around avoid circles. It is worth mentioning - if you are timing this well you should be able to drop a tower and clear all remaining nanites when Kephess is at 11% - and you should be able to almost kill him before it wears off (or at least get him into the 3% area).