Hi Anis - you write that "the 2 faces already join as a single surface" - but no that's not quite accurate. They join together into a "Joined surface" which is an object made up of several faces joined together. But that's not the same thing as an actual "single surface" which means just 1 face. The way the model structure works each face that you see in the model has its own surface underneath it, so if you have more than 1 face that means that you have more than one surface as well.

So no the surface to surface mapping would not work for applying directly to the penguin belly as you have shown there.

But there are a variety of things you can still do - since that area is mostly curved just in one direction probably a curve to curve flow would work for that area rather than a surface to surface one.

Also you could create a single surface across that area by various techniques like projecting some lines onto there and the lofting them.

Also at some point I want to add in a tool that will let you merge 2 surfaces that share a common natural trim edge into one larger surface.

- Michael