That is the proper distance from the wall. Not sure why you say, "on center from the stud" though, We usually state the rough in as 12" from the finished wall. Many folks are a bit confused by rough in measurements. A toilet rated as a 12" rough in, actually needs less than that. (Never more than) This allows for a bit of space behind the toilet as well as a flange that is set an inch or so less than 12". While we are at it, the flange is supposed to set on top of the finished floor...not recessed below.