Reconstructing what happened at a crime scene requires a trained eye, but anyone can evaluate whether the resulting narrative makes sense and fits the physical evidence. Briars thinks the fingertip bruises on Meredith's jaw were made by someone in a frontal position. To test that, hold your hand out as though you're about to grab the face of someone in front of you, and notice how your fingers are positioned.
It's also worth noting this, from the pathology report:
Escoriazioni attorno alle narici ed ecchimosi alle labbra. Si tratta degli effetti contusivi di azione volta ad occludere gli orifizi del volto (volta a soffocare o, più probabilmente, vista la loro tenuità, ad impedire l’emissione di suoni).
Mancano del tutto segni di urto o di compressione del volto contro il suolo.
Google translation:
Bruises around nostrils and bruising of the lips. It is blunt the effects of action to occlude the orifices of the face (time to choke or, more likely, given their tenuous, to prevent the emission of sounds).
Completely lacking signs of impact or compression of the face against the ground.
In other words, bruising on the face and jaw from a tight grip rather than a blow or impact.
Imagine grabbing someone's face from a frontal position, tightly enough to leave that kind of bruising, with your hand positioned so the fingers are on the underside of the victim's jaw. How believable is that?
Then position your left hand as though you're reaching around to grip the face and cover the mouth and nose of someone who is facing away from you. Notice the position of your fingers. Then look at the photo on Frank's blog.
Common sense goes a long way in this area.