Splop and/or Flow along surface

Can’t figure out how to use Splop or FACS and have a result with a uniform cross section. Splop objects show as solid even though they are thin open back shells. Object is to print with a uniform cross section.

Hi - please provide a 3dm file as an example of what you are struggling with.

Object is to have stl on surface with a uniform cross section for 3d printing and ulimately precious metal casting.
head on surface.3dm (19.1 MB)