A different approach based on the membrane will be somewhat spherical in the center, and axisymmetric. The result is a curvature continuous polysurface. BulgeDC01.3dm (710.3 KB)
Create the frame and a arc from the center of the bulge to one corner of the frame. Revolve the arc for a surface with a circular edge.
Create a trim curve, ArrayPolar the trim curve, and trim the revolved curve so that it has a scalloped edge.
Create a profile curve in the center of one scallop using BlendCrv with curvature continuity to the edge of the scallop.
Sweep2 the edges of the scallop with points at the ends and the profile curve in the center. Use curvature continuity along the scalloped edge. ArrayPolar the swept surface. Join to a polysurface.