Only thing I will add....for Pauls benefit mainly, though frankly he doesn't need any shooting lectures from me looking at his sporting achievements, head forward locks the gun in tight, stopping arm movement creeping in. If you are a higher injury seated shooter, or have limited movement through your back or core a head up stance with head slightly further back allows you that little bit of arm movement needed to get the big angles. Your head is also closer to the pivot point of the gun in your shoulder for the lateral movement, hence your face stays more in line as the gun moves. For able bodied swinging with arms is a big no no, for us disabled shooters it can be different story.
