Hey, Rusty;
Here is what I found. When I was in my beginning, throw-the-top-on-the-floor stage, I used the Ripcord's groove, and it worked fine. I didn't understand why no one liked it. BUT when I started learning to boomerang, I found that tugging on the string to bring the top back would wedge the knot into the groove. It would stick just enough to send the top flying over my head (usually towards my wife). The Spintastics loop sometimes comes too small so it sticks and flys over your head, too. If the knot is touching the crown, it is too tight in my experience. It seems to always work fine if the loop is loose, so the knot is closer to the o-ring than it is to the crown. I finally just gave up and took the loop out of all of mine, and now just trap the knot on all of them, like everyone else seems to.
Have Fun,
Tom