In our Quota game (3 times a week) we never went by handicap. I was one of the guys that ran the game.
We adjusted after every game. It’s been a few years now, but I believe it was something like if you came in plus or minus 2 of your quota, your quota didn’t change.
After that we had a system for going up or down. Took a while for us to get it right. Not sure this is applicable to your game. Handicaps are subject to both sandbagging and vanity.
Vanity handicaps are just screwing yourself, but knew several whose ego was too big. lol. Plus not everyone keeps a handicap.
I would say in your case I wouldn’t allow arbitrary handicap adjustment. I would just let their play determine the handicap.