Not sure about this theory, but I just came across a rare pack on the Cathedral Level 4 zone after I left the Royal Crypts and got lucky enough to get the Yellow Elite skeleton to spawn up with his minions that shoot fire arrows that explode at you. Well anyway, if you stand on the stairs (if you have that spawn) and close to the portal they can't hit you.
Although getting these type of mobs to spawn in the right spot will be very unlikely, maybe this idea can be used for other static mobs in other zones. Or even kited to said types of stairs. Let me know!