if anyone has ever tried diving frontwards over the high jump bar?

Wasn't that called the Western Roll? The reason the Fosbury Flop works so well is that it keeps the centre of gravity below the bar. Simple ballistics, less force needed to gain height (of the CoG). The bend of the legs or something. Mind you, it is largely facilitated by the landing surface. 100 years ago it was sand and not that deep, jumps originally were from a standing position.