You can use any size shrimp to start as long as you cut them as small as the thickness of your patty. And it is best to start with uncooked shrimp.
My stepfather’s name was Shirley=though everyone called him Al or Mac (McHenry). He had the misfortune to be born a few years Before Shirley Temple, famous child movie star. I guess in West Virginia Shirley was given to boys as well as girls ... though his dad was named Okie Olie so perhaps it was just an Appalachian or English thing ...