This may seem like a strange question but take a moment and pretend to take a big bite out of a burger.
What does your head do? Where do you put the bun? How do you take a big bite?
The motion of a baby latching well looks a lot like the motion of taking a big bite of a burger. Your baby's chin is on the breast, then his head tips back as he latches.
When your baby is latched well, his chin will be deep into the breast. A deep latch ensures that your baby gets plenty of milk and you feel no pain.