I couldn't really tell you. Maybe no one other than the software designer could. However my feeling is that the same fit is an optimal place to start for anyone. If you're not "anyone," you don't need a fit calculator. You'll order exactly what you know you need.

OTOH it's sorta like the fairy tale about the giant who made everyone fit the bed rather than the bed fit the person. They assume normal flexibility and no specific grudges against the standard road fit, which has been a standard for so long that the variation you chose is called the Eddy Fit, though as a standard it goes back over a 100 years.