I used to strafe out of the puddles, but decided it was more fun (and less dangerous) to occasionally hit my follow macro, let the tank lead the alts (and boss) around the battle area while parrying and thrusting, then hit the move backward and spread out keys to resume DPSing. Fire off a few shadowbolts, then do the follow thing again. My priest is specced for Holy Nova, which I find to be pretty sufficient for this fight. I do this for the ethereal boss in Violet Hold too. He leads you on a merry chase throughout, so instead of getting tricky with placement, I just indulge him and chase. Nooo problem.

(Mind you, I run warlocks, not mages, so I probably have at least Curse of Agony if not Corruption, and a pet beating the boss down during the follow parts -- you'd be doing less DPS overall, unless you're specced Fire or have your elementals out or somethin')