Actually, from what I have seen lately, the weird flats looks to be more like a diffraction effect from the microlenses rather than cooling. I have the ASI294MC (Which I am just about to sell as I replaced it with a 2600MC, and soon to arrive MM)
Apparently though the right filter a mottled patch in the same shape as the pattern on flats is visible if you take a photo of the face of the sensor.
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