Quote - Human beings have one basically common measurement. If you take two parallel lines, one at the top of a person's head, the other at the point of a person's chin, it's going to be about 9 inches (23 cm) no matter how large or small that person is. (standard adult, no precluding medical conditions)

I adjusted the size of various female Poser characters (no anime) so they all adhered to the 9 inch standard. here is the resulting list of their actual heights and the percentage I had to adjust them:

The sizes with the head adjustments really makes sense to me. Thanks for the comparison!