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Martin, your experience does seem overly complicated, certainly more so than my (smaller) CMOS cameras (each ZWO btw).
I don’t fully understand the logic of QHY’s gain modes. ZWO just plots it along a linear scale, and at gain 100 the camera switches to HCG mode, with the subsequent drop in read noise. FWIW, the ZWO camera doesn’t drop below 1e, although such a property is not unheard of - the IMX224 exhibits this at higher gain.
Since most CMOS chips (at least, those in the astro market) have on-sensor amplifiers, the noise introduced can be somewhat disconnected from the signal reading itself. This is the same as the ISO-invariance we see with Sony/Nikon DSLRs/mirrorless cameras.
Looking at the plots for the ZWO ASI6200, I’d probably be picking gain 100 pretty much every time...there seems to be a tiny amount of dynamic range sacrificed for enabling of HCG. In “traditional” use - from a dark site, especially with a fairly fast scope - then gain 0 would give maximum well depth and a read noise of ~3.5e...still pretty respectable. The best choice will depend on your preference with respect to dynamic range.
The offset value itself has a minimal impact on dynamic range...if you increase the offset such that the median pixel value for a bias frame shifts from 200 to 400, this is almost negligible difference with a well depth >50,000.
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