I am puzzled by the very large ADU values of the QHY bias frames.
The QHY163 is a 12bit camera (possible ADU values from 0 to 4095). On the other side, ASCOM specifies (more or less, this is another story) that the image must be 16bit, with ADU values from 0 to 65535. For that to happen, the ASCOM driver simply rescale the ADU vales coming out of the camera, by multiplying them by 16.
If you (or the manufacturer) now set an offset of let’s say 100ADU for the camera, this will show as 100 x 16 = 1600ADU as delivered by the ASCOM driver.
On a side note, the moment this signal is read into PixInsight, it will be once again rescaled to floating-point (values between 0 and 1 with a lot of decimal places). You can tell PI to present these values as 8, 12, 14 or 16 bit (and some other) values.
Regarding binning 2x2: if life would be perfect, after binning we should get exactly 4 times the unbinned offset value. It is not perfect, only close to.
It gets even stranger for dark frames. Dark frames at 30 sec, 90 sec and 180 secs all show the same values and those values are the same as the bias frame values.
For all CMOS cameras and almost for all CCD cameras there is an internal function to subtract an average value of the accumulated dark current (based on some hidden pixels who never get light exposure) from the image, before it being output. You basically never see the accumulated dark current, only the noise of the dark signal (both fixed pattern noise and random noise). The fixed pattern noise will be removed (well … almost) during the calibration process by master dark subtraction.