Thanks Rubio95.
The “division” or “shadow” of the lower cheek took me a while and I made an educated guess. I went for shadow, it matches the cast angle and grey tone seen in the rest of the illustration. Also on close inspection the dark part runs a bit over the top of the circle on the left-hand cheek. If it was a separation that would seem odd, however a shadow could do this.
There are more inconsistencies, on the side elevation of the helmet the range finder is dead center of the helmet, but the frontal/quarter drawing shows it to be positioned more forward above the cheek. Again I had to choose and went for the forward position.
It can be brain wreaking to build a 3D model based on sketches, but it’s also fun to witness the study and evolution process of the designer.