ya what lance said, it all depends on landing mechanics and rebound height.. You can use boxes that are a bit above the "optimal box height", as an overload stimulus, for sure.. you just can't do it if your landings are compromised.. if there's excessive caving in at the knees or heel is just slamming into the ground hard, then that would be too high.. but if technique looks good & the athlete feels fine, for sure you can use a box height that challenges their rebound height.. anything well below SVJ height for the dj rebound is too much, but anything slightly below, AT, or above SVJ is fine imo... slightly is ~1" or so.
peace man