You can move a little within the circle that you teleport into without starting the combat dialogue. This helps a lot with targeting the mirrors with Impalement spell and my archer could also target the mirrors and destroy them.
Another trick that helps prior to initiating the fight is that I used my rogue's teleport spell to move to another location. This immediately starts the dialogue leading to combat, but my rogue was not locked into the dialogue, therefore he could freely move around the arena and cast spells. He teleported the other party members around, spreading them out to limit the damage and he also teleported the first mob far away before starting the fight.
