[The_bluester (Paul)]

How does the histogram look on the individual flats? What ADC to target can depend on how the software samples the image. I cant comment for APT as I didn't get advanced far enough to start using flats when I was using it.

If it would not be such a massive transfer I would suggest flicking me your full set of files and I can try running them through Astro Pixel Processor and see what kind of result pops out the other end. If you package up the whole box set of files (Lights and all the individual cal frames) how much data is it? It might be doable via Wetransfer. I think you can transfer a gig with the free version.