1: Touch twice on a given side so that the skew in the probe can be calculated out. Two touches on the side provides enough information to be able to determine the angle of the probe. It is very unlikely to be exactly aligned with the machine axis. A single probe on two adjacent sides cannot directly place the corner between them unless you assume the block is perfectly aligned with the machine axis. Two probes separated by a short distance (1/2" is probably enough) on each side can. “Touches” in the next two suggestions assume that a “touch” is a pair of these to properly locate an edge.
2: Automatically compensate for belt stretch at install time - with the known size of the probe, and known end mill, and known skew in the probe, you can easily tell what the adjusted steps/mm should be and just set it appropriately. This would work for x/y, but Z might not be accurate enough with the small offset at the underside “ledge” as designed. An additional deeper pocket to probe into might be helpful. Making this process easier (ie. happens automatically every time anything gets probed) would keep machines calibrated pretty much all the time and probably reduce a lot of support calls around belt stretch. Any time you can make things “just work” it reduces calls and makes people happier
3: Automatically measure tool diameter - once calibrated as #1, measuring the block could tell the software exactly the diameter of the tool, and make entering the tool in the “probe” dialog unnecessary (touch near side of the probe, touch the far side, the excess is the diameter of the tool).