I set the arm where I wanted it and made the guide to match that location. I really have no idea what the dimensions are, just that they’re right for my gouges. They’re just made from scraps of Masonite/hardboard.  Two points touch the grinding wheel, and the other end sits in the V.

Since they register off the surface of the wheel, they actually set the distance from the wheel to the V.  Other jigs (like stop blocks) only set the extension of the arm from some point on the grinder stand, and thus will set different grinder angles if moved to another wheel or grinder that’s configured slightly differently. So I can use these on either side of either of my grinders and get the same setting at the wheel. I can also take them to a friend’s shop and setup their grinder for my gouges.