well I still think it is the simple calculation.
Take my stats example.
3233 files / the top port. (IOFOTO) 14751 = .21849 * 100 = 21.85% which is exactly my port. exposure.
the number 2 photographer,
Monika Adamczyk11619 / IOFOTO 14751 = .78767 * 100 = 78.77%
can't be much simpler than that.