Setting for "Acceptable" quadratic AF curve fit?

There is indeed. If you are using 4.5, it’s been added to AF settings UI. If you are still on 4.4, you have to use a secret variable.

See here for SGPro 4.4:

https://forum.sequencegeneratorpro.com/t/autofocus-parabola-fit-is-making-the-af-routine-fail-even-though-theres-a-clear-minimum-in-the-v/23661/4?u=ken

and here for 4.5

SGPro Minimum Quadratic Fitness - Sequence Generator - Main Sequence Software