Why is it that my Gentoo setup displays 10pt fonts the same size as my Mandrake setup displays 13pt?

I have triple-booting at present, Gentoo, Mandrake 10.1CE and Windows98SE.

Gentoo and Mandrake both use the same /home partition. They share my KDE setup files. But font sizes get translated differently in one compared to the other. Is there something I can adjust to even this out?

EDIT: There is another side to this: I have both KDE3.3 and XFCE4.2RC1 installed in Gentoo, and XFCE displays KDE/Qt-based windows with smaller fonts than KDE does, but other than that uses all the KDE rules I set up correctly.

These things are annoying to say the least!