ZWO publish graphs that are very useful for picking Gain and offset settings. Here us an example,
Just scroll down to the graphs.
https://astronomy-imaging-camera.com...asi1600mm-cool
You can see that Gain is marked at about 139 (ADU), and is usually referred to as Unity Gain in those cameras. We used to play around with different Offset figures (like 20), when these cameras first appeared, and I believe ASI cameras now come with a fixed Offset (others may comment further on this). I used to shoot alot at Gain 139, and Gain 76 (which seemed to be a good compromise setting where well depth is better, Dynamic Range slightly better, and noise was not significant enough to be an issue. Now I believe ZWO fix Offset in the driver, but again I could be wrong, as I sold my ASI1600 a couple of years ago.
A IIS member (Shiraz, aka Ray) actually published a series of charts for various ZWO cameras and he worked out an ideal ADU target, which i recall was around 600-800. I suggest you contact him as he was the expert on the figures for a range of ASI camera models.