The AKC in this country decides what breeds are placed in what categories. They also decide what is a "miniature" and in Beagles' case, they show the different sizes under two separate categories, even with just a 2" difference. There's the 15-inch, which must be taller than 13 inches, but less than 15 inches at the shoulder, and the 13" which can be from 13" to almost 15" tall, so the names sizes seem to depend completely on the breed standards set by the official Kennel Clubs.