im not 100% sure, so dont bag on me if im wrong. but when guys go up to the jump and stop on the lip theyre trying to get the speed down for the jump. also if your worried about not clearing or over shooting follow somebody that you know clan clear the jump . so you can either hit the jump with them or just pull off to the side, so you can get a feel for what speed you need to be at.
So what I do is hit the jump 2 times, even if I don't know the speed. The first one I go in as fast as I can and I usually overshoot and land flat, and the second time I go really slow and usually end up casing it. So after I've knocked a few teeth out I find a speed in between those past 2 jumps and it's spot on most of the time, good luck!