Hi Andrei, is it possible for you to upload the model file that you seem to already have there so I could take a look at your desired shape a little bit more closely?

In the screenshots you posted it's kind of difficult to see the form of that lower area with that darkish environment map on it.

Maybe you're looking for something similar to this:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4880.1

- Michael