Dark frames not so dark

[saturne33]

Hi from south west of France,
I'm using the Horizon II color and I constantly noticed the same image pattern on all my dark images.The top and bottom edges are significantly lighter than the rest of the image. This is also the case on the right edge, excepted in the middle.
This is very well visible on the attached inverted (negative) example took at 45 sec. cooled at -5°C.
The brightness of the lightest areas is double as compared to the darkest.
I saw a very similar image on another post ("Noise and poor sensitivity..." posted by bribon on Nov. 10, 2021).
It is difficult to consider that as normal  ... Any one else with the same kind of dark frames ?
Any remedies ??
Thanks !

[saturne33]

Hello. I have been in contact with Atik support (very reactive, thank you!). They advised me that the glow along the frame borders is related to the 'Exposure Speed', that should be set to 'Power save' instead of 'Normal'. And indeed there is a clear improvement, visible for example on the right dark frames in the screen capture.
Please note that the left dark frame is shown in 'negative' mode.