well i have done it three times now
and everytime i have used different settings
the first was a default attack to the back of the neck...about 5 bars
Every time his head flew off it was on the first "bounce"
then it kinda warps back at the end.
the other two times i kinda kicked him off the side
i would place a kick his right thigh and his head would fly off (again on the first bounce) then he would go flailing off the side of the stairs about half way down.