Milimetr, Two things here. One how much the belt is stretched and two how much horizontal force the belt puts on the platter. Too much horizontal force hurts the sound.
With a one motor AC these both change together as you move the motor farther from the platter. It is straight forward in finding the sweet spot of enough.
With three motors the belt has to stretch around the motors and the platter. With in reason I don't know if some extra belt stretching is an issue on its own or not but I would not want to go too far. But if the over all set up places too much horizontal force on the platter I think that would be a bad thing.
With a one motor AC these both change together as you move the motor farther from the platter. It is straight forward in finding the sweet spot of enough.
With three motors the belt has to stretch around the motors and the platter. With in reason I don't know if some extra belt stretching is an issue on its own or not but I would not want to go too far. But if the over all set up places too much horizontal force on the platter I think that would be a bad thing.