This is just an example of using blend to make a varying blend ( R5 ~ R15 ) between two complex spline irregular surfaces.
First make an intersection curve between the faces. At each end of the spline curve, sketch either the small or large circle. Blend between each circle using the intersection curve as the center line path making a wavey varying diameter cone along the final edge. Cut each surface using the same solid edge cone. Finally, blend between the surface edges with tangency.
Tangency angles are good at approx 0.02 degrees
Of course it's not automatically made, but the end result is visually beautiful and accurate.