I look at drop this way: how many inches are from the center of your shoulder to the center of your cheek, when your rear gripping arm is held up like holding the wrist of a rifle? That is the amount of "drop" of your body. Many people also lift up that shoulder, and/or tilt their head down to meet the cheek piece. But you don't have to that much, if the drop is more. It varied over the generations depending on recoil of the caliber, if shooting was more offhand or from behind cover (like a trench/foxhole), etc.