Get the box height so that the thigh at the hip is 1" below the top of the knee when sitting on the box.
Start around 60% of full-BSQ 1RM. Try to move it fast without tipping forward first to preload the hams etc.
The second week at the same or even more weight should move much faster. I usually add 20lbs per week for a while after that unless I feel a definite loss of that speed. I do something like 8×2.
im talking bout during max effort work on the box, would you take 97% of ur regular squat and use that for ur max effort box squat work.