I agree with all of You.

93mouse's picture from Richardson's book is interesting. It leads to believe that any shot into the central vertical axis of the buff will be dramatic.
One great asset is the low dipping spine that enables to nail the buffalo from brain down almost half of the chest. I will suggest that the brain location can be deceptive. On any animal the brain is rarely above the eyes. More over, a shot at the forehead could be deflected. IMO opinion never shoot above the eyes line. Between the nostrils will be safer, the bullet smashing the spine that is a longer target.
One can notice that under the spine is a gap occupied by both lungs and that the heart is below. In this zone, a bullet can whizz just between the 2 lungs and do far less immediate harm.

Fundamentally, the trouble is to center the bullet onto the vertical central axis as shows 93mouse's report.

Mouse, I'd like to know why the buff was knocked on his front feet when hit under the chin, though the bullet went in the left lower jaw. Spine commotion?