Game Mechanics: Mob hits on flat vs uneven ground

[Gatorsmash]

Grinding in the Feerrott on the skellys in the corner, there was a clear difference between fighting them on an angle and pulling them to flat ground. Blue to me at lvl 8, if i pulled two they would kick my ass on an angle but the second I moved to flat ground (it almost flat) I would crush them. It's very odd. I was there a long time its easily repeatable. It's like they are hitting you from behind in the damage. Didn't matter if I was above them on the angle or below.