While aiming at something in third person when you toggle to first person you will be aiming at something considerably lower. If you aim at something in first person, and toggle to third, your dot is much higher.

This is a very big problem in 3rd person. If you have not noticed if you put your sight dot on something like a zombies head in 3rd person, your character stoops and punches them in the chest. To punch a zombie in the face in third person, I have to aim well above their head so that my character doesn't bend over and punch in a downward vector.