It seems weird pets would consistently be causing parries since they default to attacking from behind.
I believe the whole Icehowl issue comes from the room being more ovular than circular. There were parts of the room that we consistently had people escape from, and then there were parts of the room where people would get smashed long before they came unstunned.
When we started to try to get people to congregate near the mob-entrance we finished the fight easily. I think that tends to be the longest distance Icehowl has to travel. Even if I'm wrong with that assumption there still exists one reason that using the wall would theoretically give you the best chance of escaping: it is the only part of the room where the wall is straight. This allows you to truly move perpendicularly to the charge path. Most of the other room locations require you to move at approximately 45 degree angle to his charge.
I would also recommend using left/right mouse to move forward then spin your camera. Holding strafe/forward doesn't work straight out of stun which means you have to spam the button, but left/right mouse button does.