I 'm sorry for the delayed answer.
I 've tried your nice idea but unfortunately it doesn't work, or maybe I do something wrong. In the new file I have a hidden layer of the circle, that I 've tried to move the circle inside the letter as a controllable element with the alpha mask of the letter that you told me. It doesn't work too. If I could set the boundaries of the letter so the circle remains inside the letter, maybe it could be a solution?
drag on a specified path new.hype.zip (63.8 KB)