Great example the kicker's momentum is moving forward not up. His whole body is behind the kick.Here is skip lead leg. I think you can get more of your weight to travel toward the target a greater distance more easily and coordinate that movement with the kick to ad power as opposed to using the rear leg. I think the difference may be in the skip with both feet on the ground as opposed to simply pushing off with one foot as the rear leg moves forward. I have no scientific justification - only experience.