It was mentioned a few times about having a nebula in the frame possibly throwing things off a bit. Between that and edge of field optical distortions, I settled on an annulus configuration of 15% / 55%. This gives me a nice donut that avoids the center of the field where a nebula might be, and the corners of the field, but still has plenty of star quantity inside the large donut. I have full field checked with this configuration, and it seems to work quite well for my needs with the linear algorithm.

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