I never tried to think it through to the degree that you have. I remember and have taught my Son to aim for the opposite front leg on a quartering shot. He was taught to go 1/3 up the body following the front leg up on a broadside shot. With the animal quartering to or from you if you use that hidden from leg as your aiming point the bullet will travel through the boiler room on the Deer heading for that leg.
You taught your son well!