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With the QHY products do you need to play around with the Gain and get that right. The aim is to have pixel full well at 65535 ADU or at least as close as possible to it. On my QHY9 via ASCOM this occurs at a Gain of 21 and Offset around 106 (gives a bias of 930 ADU).
If you have your gain and offset done correctly (mostly gain) you know that you have hit your full well capacity when you have 65535 ADU. The reason you want full well capacity to be at 65k ADU is that it gives you the largest dynamic possible which is your ability to capture both bright and faint parts of an image.
When referring to hitting 45k instead of 65k, this is for your target. Lets say that you're imaging a relatively bright nebula (not as bright as Orion), if you can keep the brightest part of that nebula around the 45-60k ADU mark that region will be bright but it will not be saturated.
When it comes to stars, if they are saturated, they will appear white as everything is at max value. So if you want star colours you do need to keep away from full saturation.
The "auto" sliders should just be do to with screen stretching (white and black point) for visually looking at an image and are not always helpful when trying to ascertain whether a part is saturated or not. An example of this, opening up a 5s sub in Maxim DL of M42, because it has such a large dynamic range, the whole core region will appear blown out under a Medium stretch even if it only has a maximum ADU value of 5,000. So screen stretches are not always good indicators of saturation, you do need to look at the individual pixels.
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