Yeah, seem that there are two different issues, or two lines of sight on the same issue.
1) how to generate a flat field as assessed by software, and
2) how to generate a field that appears flat/well corrected in images.
For me, with my relatively lazy/economical attitude to the hobby, there are enough things to get "right enough" to make images look "decent" (especially as a beginner) so I wouldn't chase any imperfections that only software can detect.
I read a post by Daniel Mounsey the other day discussing similar, that we as beginners often get hung up on numbers and hyper sensitive metrics, where as in reality it doesn't make much material difference.
That said, I applaud your effort here, and if you do find a magic formula for spacing, I'd apply it for sure
(oh, and I will supply some single star field subs as soon as the weather clears)