Shadows derived from Shape from Shading.
A good example of how shadows might form additional evidence.
Here I have inserted the outline of the shadow from Steve Wingate's SFS photo.
Note how part of the helmet wall doubles as a helmet for the silhouette face. Also one can see a faint shadow in about the right place for an eye.
From here by adjusting the angle of shadow one might be able to make the silhouette line up exactly with the ridges just inside the face edge shown in red, even the line in blue which are both similar to the shadow edge. These might happen at symbolic times of the day or year.
Another possibility is the shadow may line up with these geometric shapes, from mounds in this area.