The cut calculator (https://jscalc.io/calc/QHWZUpKFJzyGVS2D) lists a minimum Z axis of 70 mm, with leg conduit length of 57 mm. I believe the minimum is due to the height of the foot and the “lock-corner” that gives it a certain minimum height.
If you really want lower Z-height, you can prop up your workpiece. The tilt of the Z axis (away from vertical) creates more deflection than the deflection of the legs, so propping up the workpiece will help if you really want the absolute minimum deflection.