Fat to Muscle Ratio

Hi Coach. I was reading up on Scott Stevenson after you mentioned him. I noted with interest his comments around fat to muscle ratio. Basically, he states for gaining mass a 3:1 (fat/muscle) is normal, but with proper diet, recovery, etc this can be extended to 2:3. For 30lbs, this equates to 10lbs fat for 20lbs lean tissue. In your opinion, for someone close to their genetic potential, is this still a realistic number to have in mind?