There is no correct answer. I use a blunt cut at the top of the ear where the arms of eyeglasses sit, with no taper. I have seen lower ear, mid ear, faded, pointed, and everything in between. It is just personal preferences. I have tried different locations on myself and settled in where I am for three main reasons:
1. It is easy (no fading, tapering, pointing, and the location is ease to judge.
2. My sideburns are rather "weak" so to say. So the extra hair i get by going high helps them look fuller.
3. It is easy.