I wonder if my experience was somehow based on the ASCOM "presets" in the driver and not any active calculation then. Maybe when I selected the same gain as the preset, it chose the correct offset. My gear is all packed up in the car so I can't check right now. I did find this article on ZWO talking about the presets: astronomy-imaging-camera.com/tutorials/c...in-ascom-driver.html
I saw another thread that seemed to indicate that offset can very slightly even among the same model camera, so maybe this isn't something that can be calculated after all. My apologies if I misinterpreted what was happening in my other software, but it's a backup PC that I've only used once or twice.
This could be automated, to automatically calculate the best offset for gain levels from 0 to max in steps of 10... but I personally only use 2, 3 or maybe 4 gain levels for each camera. I think I'll just go back through and re-characterize me sensors at my common gain levels.