Under Advanced a number of parameters can be set. Check RadialArcFinder for details. Here we focus on the edge detection.

We set the polarity to Light to dark since we are searching for a dark edge. The smooth base and smooth counter defines the trace combs filtering 2 and 1 is used when there is a edge with good contrast. With noisy conditions the values can be increased to detect the edge. When there are many edge points detected - the circle detection can be improved by using the Remove point closer than filter or increasing the Max Search count. When selecting differentiation = 1 ( first derivative ) the edge detection handles intensity variations as long as there is sufficient contrast.