Building the face
This is an alternate idea of how the face could have been constructed. The main idea is that the face was never designed to look face like without shadows. It was instead to be a structure to throw the most possible face like shadows so it could be seen from the air. Because of this it isn't also possible to be completely face like without shadows as well.
The start may have been to select a feature something like the top one below. Compare this to the central ridge in the face.