Ken, I fully understand that you are puzzled. I am also puzzled this morning!

I will try to explain it, but the issue is tricky, so I am not sure if I am able to fully clarify the situation. I will show it on the knife jig despite the fact that TTS-100 was not designed to work in conjunction with it.
The two metal contact discs of the TTS-100 define a tangent line to the grindstone at a point where the tool edge meets it. The position of the USB hole of the TTS-100 is for given jig, edge angle and protrusion defined by distances H and L. See the attached drawing. H is the height of the USB above the tangent. L is the distance between the USB and the stone measured along the tangent. Because for most jigs the distances H and L are different, the USB holes in the TTS are generally not usable for other jigs than the ones for which it was designed.
They are some exceptions from this rule, e.g. the already mentioned 44 mm protrusion results in a 25° edge angle for chisel mounted in SE-76 when the hole B of the TTS-100 is used to set the distance to the stone.

Ken, please do not be afraid about your approach, I am convinced that it works pretty well for a limited range of grindstone diameters. Nevertheless be aware, that it will not allow to transfer the same angle setting from T8 (250 mm) grindstone to T4 (200 mm) with acceptable accuracy.

Jan