I thought of that too, but then noticed that Raer, who had issues with Annihilate this week, was a troll, like myself. It could be both racial hitboxes and something else that happened this week though.
is the hitbox the same for all races?
I have heard of a tip for H Malkorok where people would drink Noggenfogger Elixir before the fight in order to shrink their model and make it easier to avoid the orbs in P1. I'm not sure it actually makes your model effectively smaller (as in it wouldn't hit something when shrunk, while it would have hit it in the usual state and being in the exact same spot), or just helps visually, but if the former, then it wouldn't be surprising if race had something to do with KS too.
Really not sure how to test it though. The only thing that comes to mind might be, how KS behaves on a target dummy. I'm a troll, and KS doesn't put me on top of the dummy, rather just outside his smallish hitbox. When I was a worgen, I'm not sure it behaved the same way and maybe put me closer to the center of a dummy. But I'm not 100% certain and maybe it's not the right approach.