According the specification the image field of the FSQ85 field is 44mm (without reducer). As the 16200 sensor is 27.2 x 21.8 (35 mm diagonal) this should no problem. For sure the illumination drops toward the borders. But this is no issue, as this can easily be corrected with flats.
The problem is to get an overal flat field. By design the flat field of the FSQ85 is only achieved in focus. And the tolerance is very samall. If you focus on a center star, It may be that the stars in the inner 50-75% of the image circle are very well regarding roundness, but in the corners all stars are distorted.
There were already some discussions regarding this topic.
See here:
The next step for me is to ensure that tilt is 100% eliminated. Then I can start again with autofocus supported by SGPro.
Best regards
Reinhard