Method 1:
At the first step you have to create a convex shape
surface. You should draw the wireframe for the surface and
create a skin surface on it. If wireframe contains U and V
wire directions it would be more exact (The command
AMLOFTUV is very useful).
After creating the surface it must be moved on the required
side of the part. The command AMSURFCUT -> Type option
allows you to select the Protrusion to fill the space
between part and surface (Selecting a work point is not
necessary).
Notice:
All boundries of the surface must locate in the interior
side of part. Therefore you may need to create the base
part larger than final required size and after producing
the protrusion, slice sides.
Method 2:
1. Create the solid with convex face which Rx=Ry.
2. Create a block from the part.
3. Insert the block with different x and y scale factors.
Notice:
In the second method the inserted block cannot be exploded.

Farzad