Originally Posted by Kontact

No, it doesn't. The outer width is based largely on the way the saddle curves away from the top portion you sit on. Some saddles have large tops that quickly drop off the sides. Specialized saddles do not.

I appreciate the way you are trying to approach this with an eye toward metrics, but saddles don't really work that way. They aren't designed with pelvic tilt angles in mind. You don't sit on your 'sit bones' (ischial tuberosities) but the narrower ischium. And which part of the ischium you sit on is not something you can find out without a pressure map, because pelvises are actually much more varied than you might imagine. I know for a fact that people with sit bones exceeding the total width of the saddle they are riding because they aren't sitting on them. Saddles aren't kitchen chairs.

On top of all of that, the soft tissues between the pelvis and saddle also vary greatly in thickness, density and sensitivity. For instance, some riders greatly prefer angled sides, others need a flat surface. There is no rhyme or reason to that, because bodies and preferences vary too much to treat saddle selection scientifically. All you can really do is look for a saddle that meets many of your basic needs and then try it out.