SetRange for closed Segment

[tairoark]

I want to run a CurvyGenerator to get a mesh on just the 'closed' part of a curve (what is filled in between the last and first CP's.
I'm using InputSplinePath.SetRange. However,

SetRange( null, null ) generates the whole mesh
SetRange( lastCP, null ) generates the whole mesh
SetRange( firstCP, null ) generates the whole mesh
SetRange( null, firstCP ) generates the whole mesh
SetRange( null, lastCP ) generates the whole mesh
SetRange( lastCP, firstCP ) generates the whole mesh with warning
SetRange( firstCP, lastCP ) generates all the mesh excluding the closed part