Hi Pilou,

re:
> The "Add Sync Points" button ?

You can use that to control how the blend is connected between the edges.

Here's an example:


The default method where the blend surface matches percentage of distance will make a result like this:




If you add sync points on each bump you can get a result like this:




Basically for the first way the blend surface is made up of isocurves like this:



With adding in sync points you can influence it so the blend surface is made up of isocurves like this instead:




- Michael