Hey Kins,
Thanks for taking the time to review this product! I'm so sorry you weren't completely satisfied with your glass screen. I do see how one with a 'nub' as you say, would maybe sit into place better! This is meant to be wider to cover a range of different sized bowls.
I would check out the Smojo Permanent Smoking Screen. It's going to stay in place a lot better over the glass version.
Let me know if you have any other questions or concerns.
Best,
Sarah Brown
The 420 Science Help Desk