the farther you lean forward, chances are, the longer it will take you to stop. the whole idea in leaning way forward is to take as much weight off the rear so that you can sustain the skid for a longer distance.

that said, if your skid seems jumpy, it is probably because your legs aren't fully locked causing the wheel to lock, push your legs a bit, lock, push your legs, etc. on a harder gear, you may have engage in some fencing with your stem in order to do this. on an easier gear -- or with stronger legs -- you may find that just unseating yourself and locking your legs while nearly vertical is sufficient.

one last possibility is that when you're skidding you don't maintain control over the bike well so that you wobble all over the place. two possible suggestions -- 1) skid with your hands on the widest part of the bars (you can do it with your hands at the stem, but if you're having trouble, this might help) so that you can control the front end better, and 2) locking your thighs against the stem and bars in order to keep your front end pointed directly forward.

hope this helps.