That's going to vary by tank of course, if you're used to playing with tanks that you can throw a brick wall at the mob without it blinking your direction and then get one where if you sneeze on the mob you have aggro..
I've also had runs where it didn't matter how easy I went, I've still nearly pulled hate off mobs (quelling or not) with every pull.. main thing then ends up being don't run around like a chicken without a head
(unless the tank is dead ^^
As far as the 50% figure it doesn't seem that high from the little bit I've paid attention to it. I miss 1.0 Chameleon though which was a straight dump all aggro skill.