FSA compact handlebars (Wing Pro or Omega) are measured on the end of the drops, c-c. But their width on the top/hood are shorted by 2 cm.

My Fuji Finest RC (XS) comes with a 40 cm handlebar that is compact one but is measured on the top/hood => the width of ends c-c is 42 cm. That's a little too wide, I think, for a XS frame. Recently I ordered a FSA Omega 38cm, which should be fit for my shoulder according to an article on Bicycling.

Why don't the manufactures measure their handlebars in the same way?