I do bottom position Zerchers but they are not from the ground.Generally mine are on blocks and the bar is roughly 15 to 18 inches high. I use them as a Conans Wheel accessory .It certainly isnt a lift I would do for a max.I think 185 is the highest I have ever gone on them .
There is a way to get this going if you don't have a rack... Deadlift the bar, hitch it by squatting down just below parallel then throw your arms under the bar and come back up...