How each technique clears the bar
The flop is a back-first clearance: the jumper approaches on a curve, takes off with their back to the bar, and arches the hips up while the shoulders and head clear first. Because the body bends around the bar instead of rising straight above it, the center of mass can pass close to bar height rather than well over it. The scissor kick is a straight-on, feet-first motion: one leg kicks up and over while the trunk stays upright, so the whole body has to clear higher than the bar. That difference in mechanics is the entire gap between the two.

