The problem isn't fixed pattern noise (FPN), but rather the changes in the calibration that then affect the dark fields and the amp glow. If you can't remove the amp glow with darks then it makes long exposures pretty difficult to process. Thus, if the internal calibration changes then the darks change and you can no longer remove all of the amp glow.
I've seen some pretty big changes in the darks within just 24 hours, so it may be that you have to take the darks at exactly the same time as the light fields without making ANY changes to the gain or exposure.
One of my guesses is that if the first internal recalibration is done before the camera has reached its temperature set point then there will be an offset that could be as large as something created by a 40C degree temperature delta, making temperature regulation kind of pointless (for the calibration subs).
I guess it really depends upon when the internal calibrations are actually done, does it only happen on a power cycle, does it happen with every gain change, does it happen with every exposure change? Furthermore, are there different levels to the calibration (some only done on power cycle, others done with every gain change, etc.)?
Thus, I'm wondering whether there is some kind of software reset that could trigger a complete set of internal calibrations within the sensor/camera. So, the process would be that you let the camera get to the temperature set point and then you issue a reset to the internal calibration. Maybe you could force that with a simple gain change, I don't know.
