Kris,
I asked this same question three days ago, but didn't get any response. After looking at the cues here and further experimenting, I've decided that for me "play chicken with the KB" results in a much shallower hip hinge, my wrists contacting the iner thigh and the overspeed eccentric causing the bell to rotate up and thump me in the rear.
Fixes for me are 1) use a heavier bell, the thumping only happens with the 16kg; 2) be less dramatic with the eccentric, go about 80%; 3) forget playing chicken and hinge normally.
Hope that helps.