Since the bigger ball has more parimeter than the small one it takes a longer time to make a revolution making it look like the bigger ball is moving at almost the same speed as the smaller ball with a faster motor. Ex: Say I take to mirror balls one 12" and one 16" and they both have the same motor that pushes out 3 RPM per minute, which ball will go faster? The 16" why? Because although the motors are pushing out the same speed the bigger one has more of a parimeter and when there is more parimeter it has to make a bigger revolution faster than the small ball that makes smaller revolutions. If you add extra speed to compinsate the smaller size you can match them up. This is why you don't see many 6 rpm motors that can support balls that are 16" and above.
The mini star ball will still will be going faster than the bigger one. I was just making a comparison for him if he saw the bigger one about how it would compare in speeds of the smaller one.