Placing the adjusting screws in the corners works great on a 3 point mechanism as 3 points of contact create a plane but when using 4 points there is always going to be a screw either in the way or not contacting the camera clamp like a short or long leg on a 3 leg stool vs a short or long leg on a 4 leg stool.

When using a 4 point unit you will want to use two opposing screws as pivots such as the left and right (x axis or y axis) to act as a hinge and flatten the field by tightening the top while loosening the bottom and by doing it this way then there is always full screw contact.  The axial design allows the pivot points to be on axis without the constraints that are created by the off axis torque that is a byproduct of the radial design.

To adjust the z axis for back focus, leave the y axis screws loose and adjust the x axis screws in or out until the HFD is at a minimum then adjust the y axis screws to flatten the field and ASTAP works great for this purpose.

When using Hocus Focus, you should use the corner numbers to picture which way each side of the sensor is out of plane and adjust the two sides that share that corner and by doing so there will be full contact with the screws.  Another way to achieve this is when using HF is to rotate the camera so the X and Y axis's are aligned with the corners of the sensor instead of the sides.   If you adjust just one corner on a 4 point system then we are back at the 4 leg stool conundrum so use of the hinge effect becomes mandatory.