What makes a tubular shape transition from surface to polysurface (brep)?

[zoster (Andrei Raducanu)]

Hey all!
I have a filleted polygon that gets offset (towards the center) and then lifted then i make a loft surface from the two curves.
If I change the offset value from 16 to 17, it becomes a polysurface, rather than a surface.
I would like to learn what determines this shift, if anyone can help me out.
Mention: if i offset it on the outside (make it larger than the base curve), this problem doesn’t occur.
Many thanks!

surf vs brep.gh (28.9 KB)

[Joseph_Oster]

Here is another way to explore that idea with polygons from three to 12 sides.

surf_brep_2019Dec11a.gh (10.3 KB)