There was a question about this in https://makemusic.zendesk.com/hc/en-us/community/posts/1500000000062-help-on-rests-collision?input_string=collision%20rest

But, would it not be better if rests, by default, don't collide with other rests and notes? So if I enter a rest in layer 2 it would always be inserted beneath the note of layer 1 etc.