I carry this saying as my signiature to try and bury it in my brain.

Once upon a time I didn't "aim for the exit" on an animal that wasn't so much quartering away as he was foreward of my position. Still looked like the standing 3-d target in my backyard(perpendicular to me), but not directly next to me- foreward of me. This equalled an illusion of being broadside when in fact he needed to be shot as if quartering- the arrow entering a little further back than normal so it would enter/exit through both lungs. In the heat of the moment that didn't occur and that lesson haunts me to this day.

So therefore I say "aim for the exit hole", and yes you want the arrow to enter the side of the imaginary line facing you in order to exit the offside of the imaginary line.