Ortur Rotary Wine Glasses

Hi All,
Just got my Ortur rotary. I have some questions about how best to use it.

  1. How wide should the rollers be spread apart in relation to the diameter of the glass?
  2. When I use the rotary with tapered wine glasses and tapered stems, the glass wants to roll out of the stem support rollers. What causes that?

I think my inexpensive wine glasses and stems may not be perfectly symmetrical. Could that cause the problem? I also know to weigh down the glass so it grips the rollers better. Thanks for the help?