Disclaimer: leaps and other dance elements are not my area of expertise, and any pointers I give on them will generally be my dumbed-down understanding of what I've heard from people who know these elements far better than I do.
Having said that, here's my understanding:
The most crucial part of the leap approach is the final step right before the leap takes off. The final step of the approach should be long, low, and almost like a mini-leap.
Here's a brief video where Tammy Biggs discusses this: