Flow along surface problem

I used a lot this command in the past but I can’t get it to work correctly here. The result is always bigger than the target. I join a simplified version (the object to transform has a texture on it that I removed here).
I checked the Dir of all objects involved, ShrinkTrimmedSrfToEdge the target, etc…
Flow problem.3dm (7.7 MB)

(screenshot of posted file)

just to understand - and be able to reproduce your problem / question:
does your file show something like exploded view ?
or are you using the surfaces in the same position as in the file ?

the 2 black (gray) surfaces are both planar but not parallel.

_selPlanarSrf to check planarity → yes
_setCplane to Surface - first Surface
_boundingbox (cplane) - second surface → will show a box → surfaces are not parallel

does this help ?

I succeeded…
I originally created the planar reference surface derived from the target surface and it distorted the output.
The correct way is to create the planar surface from the object to flow.

No, the position of the surfaces in space is not important.