I’ve added the skull photo to to the previous drawing/face image. Now I understand what was wrong with the proportions in the forehead area: specifically the issue with the eyebrows being located on the super orbital ridge. I had placed the top of the skull too high, way too high, in my initial drawing. The super orbital ridge is located halfway between the center of eye socket and top of skull. So that’s why the green line indicating eyebrows is way off.
The vertical blue bar indicates the constant: that which I aligned all three images up with. (By the way, in the skull photo, the red band around the whole skull is a rubber band I rigged to hold the mandible/jaw to the skull itself, since they are two separate pieces.)
I’m so relieved to find out what I had done wrong, and wouldn’t have known had I not shot the skull photo and placed it here – great idea, Bob! Thank you!. I’m going to do more like this, and work with them more accurately now that I know what I’d done wrong.