Hi Heiner, can you please post the 3DM model file in it with the objects you are trying to flow? That would help a lot to be able to analyze what you've got going on, it's hard to tell specifics from a screenshot alone.

Also what mode are you using for the Flow, is it "projective" mode? If so then the problem is likely that projective mode is really meant to project a smaller piece onto a larger broader surface and there can be some weird behavior if the base plane is larger than the projection target. If any rays from the base plane shoot out and don't hit anything on the target surface that can lead to problems.

If you're not using projective mode then maybe you've got a somewhat wiggly target surface - the way Flow works is that it will generate an offset distance away from that target surface and if the surface is wiggly those wiggles will get magnified in the result. Think of the offset as being like sticking a long pole that hugs the base surface. If you then slightly wiggle the base of the pole, a small movement at the base translates into a large movement at the tip of it, maybe that's what you are seeing.

I'm not sure though, it would make it easier to give you better advice if you could post the geometry so I could repeat the flow over here and take a look at your objects.

- Michael