Oh, for some reason I was under the impression that "OnRectTransformDimensionsChange()" wouldn't be available since SuperTextMesh doesn't inherit from monobehaviour? Is it actually being called? I'll be able to check myself in a little bit. Thank you so much for your patience, both of you.
I'm not sure why you're getting different results than me, there... did you revert the changes made before?
But if this works, I'll gladly add it to the next update! Even though calling Rebuild() multiple times is inefficient, for small UI elements, which this would mostly be effecting, it's not too bad, even on lightweight platforms. But I keep wondering if there's something else I'm forgetting here, sorry for all the trouble. I'll do another check on the code shortly, but my results look different than yours, so I'm still a bit confused by it all