It doesn’t seem that it’s possible to set the radius or diameter of a circle or ring Shape 3D with the envelope modifier. Using a Null for scaling a ring also scales the ratio of id/od so that’s not ideal. Any other way to achieve this with a modifier?
This currently isn’t possible due to some internal limitations, but it is something we are aware of and looking at. If you really want to do something like this, I would maybe try making a torus in e.g blender, and setting up some blend shapes to do what your looking for. You can then control those with modifiers with Morph Controller.
I fixed it with a js node, but it is a bit clunky