Surface Extrusion along vector of non-planar curve

Hi all,

Have a number of closed curves that have been projected on to a non-developable surface. Extruding the curves does not create a solid since the curves are non-planar, so "cap" is created by intersecting crv and surface.

Both the extrusion and the translation of the cap to the correct position share the same vector source.

Process is simple but curiously the results are not the best...

Any ideas? Thanks!