- bring your hamstrings up. they're weak and that's why you're dropping on to the box.
- on most of those reps, you didn't release your hips.
- don't groove rock, ever. you groove rock every rep.
- point your toes more forwards. it uses more hamstring & glutes.
- push your knees out.
- explode up. don't "swing" the weight up.
- sit back more. shins past perpendicular. try to touch your balls to the box.
- use heavier weight. raw speed work is usually 60% - 70%
- descend faster.
- depth looks fine.
Thanks to those who responded to my request for pointers. I'll do my best to rectify the problems.