I just can't "see" this with small shot, just from G/Thumb's testing.
Now, we don't know what size "bird" shot G/Thumb was using. It looked like maybe 4's or 6's. Seems to me, he didn't get the "penetration" on the skull until the range was bare inches, not yards. 15 yards, a few pellets managed to pen to the liver, etc. At even 10 yards, there was not severe damage to the bones of the skull & on the body, the penetration barely made it to the lungs.
At 5 yards, severe damage to the skull though = devastating, just like a slug at about 75-100yards.