There is no mention of cinch length. Cinches are offered in Horsehair, Mohair and Cotton cordage in widths of 4 inches to 7 inches to complement the various saddle riggin set-ups.
I'm not sure when it happened, but today's mass produced cinches, no matter what material used, became streamlined for production. They are all limited to 3" to 3.5" wide at the buckle. For Roper cinches they expand to an approximately 9" wide leather reinforced center diamond. ~Leslie