Another thing that might help is to add a couple of extra spheres. I think this will help in two ways. It will keep the region from the top of the head from being directly connected to the shoulder and also less to the face (circled in red/green below). it will also allow you to "think cube" by allowing you to have the neck sphere protrude more from the face of the cube rather than the edge. Notice how this produces much less stretching of the underbelly (in yellow).