Showing my work:
28mm: Starting with a tall 6-foot person: 6/60.96 = .09843. .09843 feet in millimetres is 30.001 mm. A six foot person at 30 mm makes a common 5'10" person be 29.166 mm tall, which is 1.1666 mm above 28mm, which puts their eyeballs 2.79 scale-inches (as in, the relative scale of an inch to the figure) below the top of their head. That's within a quarter inch of the height difference between my own eyes and the top of my head.
32mm: Every model is simply run through a perl script that multiplies it's scale by 32/28.