Calculations of force strengths and particle masses in my CERN CDS preprint EXT-2003-087 use volumes of geometric objects whose scale is fixed at unit radius. A detailed justification for this is found in "Scaling of Wyler's Expression for alpha", by Robert Gilmore, Phys. Rev. Lett. 28 (1972) 462-464. Here is a pdf file of the material on this page.