I have seen the same problems with my guys as well. I agree with Mike about working on elastic abilities with the athletes that have the biggest discrepencies. That seems to drop the gap a little bit. I found myself doing way too many standing triple jumps and 2 or 4 step approaches without lengthening it soon enough in the year. This created a big difference among my guys with their DD and their actual TJ performance.
Very good point. Most of the bounding we do is from a static/standing start as well. We do 5 step jumps every other week (we only have pits 1 day a week), but thats it.