I don’t wait for the 3-champs to come to me…Like other posters have said, I too position my toons at the wooden door; once the 3-knuckle heads are down I run to meet the champs. I back halfway to my other toons just into their ranged attack range….then promptly head to grab a new pony. After the initial beating they give my main target the damage seems to get dispersed between my other toons since they get agro by ranged attack while I grab a new one on my main.

Hope that helps a bit.