There was an instance where I was surprised by the shot. It happened from a rough position and even though I know spin in rough is fruitless, I use it as a matter of habit. I want to say it was from 20-25 but I can't be sure. I do remember the wtf moment, though. LOL The ball acted like it was in high gear reverse.
I do know that out of 20-25, backspin on the 64W does affect it to the point where I don't use full back spin, only 1/4 to stop the shot. It wants to back up with more than that but I never tested it. Sticking with what I know. (Although now I'm going to start looking at it.) :-)