When the tank gets impaled, Anub attempts to get closer to him because he's suddenly out of melee range. He does this by centering his hitbox on yours... if you are too close to a wall, Anub "enters" the wall and goes into evade.
When the tank gets Impaled? wtf? I've not been impaled since about an hour in to our first attempts unless I got vastly unlucky and the wrong ranged dps was in the wrong place.
If you are getting Impaled more than once every 5 attempts, you need to address your tanking position.
Impale targetting range is large (as in, 10000) - Standing outside 40 yards merely prevents you being hit, but the impale still 'goes' after you. So no, its just pure bad luck. Unless the MT is being impaled as the result of someone else being impaled, which I dont think is whats being said.
Well, I got impaled and Locust casting in the same second while learning it and made a rapid decision not to do that again and have subsequently had no issues and none of this evading crap.
I put Anub in the alcove with me about 45 degrees from the meridian line to the kiting circle side. My healers/dps are all on the opposite side of the meridian line at roughly the opposite angle to me, on the safe side. The MT healers catch a couple of Impales and I never do.
The only time I've been impaled since then is when a warlock was Dps'ing on the kiting side, putting me in a line between Anub and the lock.