Hi Pilou, also for a sphere the top and bottom "poles" of the sphere are areas where the sphere surface completely squishes down to a single point.

So similarly when doing a flow anything on the top or bottom edges of the base surface will also try to compress down to a single point and so it's not so good to have something like a plane surface running right along the top or bottom edge since that will then cause that plane to be squished into a point in the deformed result.

So for applying on to a sphere you probably want to have a bit of margin space area between the objects you are deforming and the top or bottom edge of the base plane.

It will also probably cause problems if you have bits of the objects being deformed actually sticking out past the top or bottom edge as well - I can't really tell just from the screenshot if that's what you've got in your case there. If you were to post a 3DM file instead of just a screenshot it would make it easier for me to give you some better advice though.

- Michael