My philosophy is that he's sloppy.
Pine is an awesome tree to fell, one of the best. My theory is the height of the back cut in relation to the apex of the notch doesn't matter all that much in strong hinging wood, like pine. It does look rather sporadic and not in good form.
Higher cuts leave a ledge that can allegedly keep the tree from getting pushed over the back of the stump when dropping through obstacles. By the same rationale, making the back cut lower could produce a ledge to keep the butt of the tree from kicking forward when pushing low.