One and a Half Head

How does a real small difference in height turn into a fictional much larger difference and why? The measured global difference in average male and female height is about around 7 centimeters. However, in fiction on tv or in film it is almost codified to exaggerate the height difference between the sexes to the size of a full head or more, not only reinforcing notions of male physical dominance over women but perpetuating the flawed idea that taller is better. In extreme cases this leads to the huge guy, tiny girl theme.