So wen I box squat
I decend till my but hits the box.
Short pause.
The stand back up.
I never let the weight transfer.
And I don't sit all the way down.
I've seen videos of west side doing box squats and they Definetely sit all the way down.
But they are all about conjugating.
So they do a whole block where all there lifts are versions of the lift just made harder.
Paused box squats
Bench with chains
Deficet Deadlifts.
But I agree with you...letting the weight possibly compress the lower spine is sketchy.
If attempted to just have to stay tight and keep the spine in a safe, erect position.