A few days ago, out of boredom, I modified my mirror cell. I removed the 4 pieces of felt that were supporting the mirror edge and replaced them  #10 nylon screws 90° apart based on the "Mirror Edge Support Calculator". I shaved the ends of the screws to an inside length of 1.5mm. I also replaced the  cork pads with  #10 nylon countersunk washers which I shaved to 2.75mm thick. Their locations were determined by the "PLOP" software.
I really wasn't expecting a noticeable improvement. But when I took the scope out tonight for a test...wow. The edge of stars are actually smooth now instead of the little cotton balls I saw before. Didn't know what I was missing. The best $6 I've spent in a long time.
Thanks to all on CN for providing the information that allowed me to make such an improvement.