Thanks! I added an addition to the code here:
on which I based my PG, since this has the same problem.
As for the little sphere: Nice idea, and I was infact using 3-sided cylinders as rays anyway, but decided to reduce the number of faces and went for lines. A full sphere would not be great, but a tetraeder might do… Anyway, I guess the occasional full testing is fine for now.
One problem remaining for completeness is the minimum movement distance (see first post).