I'm saying this knowing that you know how to make a frame flat by putting the wrench on the high corner and pulling inward.
put the frame on the exposure glass and check for racking.. adjust till it's flat.
now on the table, the corner w/out the wrench is the leveling corner, loosen the set screws and move it down, place the frame on the table and adjust that corer up until it meets the frame. Tighten up and check, adjust as needed.
frames should now be flat.
if they are not then your technique for tightening the bolts may be off. Snug the bolts all the way around first, then torque set them.
If you still have racked frames throw through drywall, curse and hand adjust them with the wrench.