In the example below, the upper voice is upstem voice 2, and the lower voice is upstem voice 1 (and I can’t change those things, because reasons).
You can see the dot is too far away from the notehead. I can set the Upstem Voice 2 to voice column index 1, but then the notehead is off-center. It also doesn’t matter if the note is full-size.
Interesting. I played around with the voices and plenty of other combinations work correctly, but I’m not exactly sure why that combination doesn’t. I assume you’ve just adjusted “Rhythm dot X … spaces” and moved on, but it would be good to find out what is happening here.