It’s got to be the angle that is achieved by using a longer handle. Your fingers would tend to be in the bowl with the brush/handle with a shorter handle making it a little more difficult to get a steep angle to whip the brush around. The round shape probably helps out a bit also. I have heard about the shorter brush rattling around for a few people. Of course, I am waiting for both of these to arrive to tell for myself!Now that I have re-read this, I realize that it doesn't really make sense. It has to be the loft of the knot and the shape of the handle that make the rainbow less likely to bang around the inside of the bowl.