https://astronomy-imaging-camera.com...94mc-pro-color
I checked out the camera on the ZWO website (link above) and it appears to have a interesting characteristic that is seen on a few CMOS sensors (not many at this stage) and that is a dual gain mode; this kicks in at gain 117 on your camera.
This hints at what you’re describing and is inherent to your camera but not cameras in general. As gain is increased the full well capacity (FWC) decreases as does read noise. Generally read noise drops slower than the decrease in FWC which is why the dynamic range decreases as gain increases. Your sensor though has an obscene drop in read noise around unity gain which recovers a LOT of dynamic range. It’s dropping from 6e- to 1.75e- instantly so you have no reason but to use unity gain because there is no loss.