Nope, does not compute.

With four I can accurately change any of the four sides of the plate. With three I can only change the two front corners and the back. How on earth am i supposed to level one side or the other equally ?

Fortunately the knp holds calibration almost indefinitely, so it's not been a problem.
But I just can't work out how I'm supposed to drop one side vertically without also effecting the horizontal tilt, and vice versa.
It's completely counter intuitive.