Hi Metin, yes it's as eddi says above - surface to surface flow works on underlying surfaces (shrunken down as in ShrinkTrimmedSrf), it does not process something like a trimmed out notch, only the full structure of the underlying surface is used.

You can see the full surface if you turn on the surface control points on your target surface, you'll see that the narrowing edge you have is not part of the underlying surface structure but is instead a trimmed away area.

For contours like that to have an effect in Flow they need to be part of the surface's own control point structure and not a trimmed away detail.

- Michael