As Kevin Robertson has wrote in detail, you want your shot to be in the center of the vital triangle. Idealy you want to shoot the top of the heart , severing any artery’s as well as passing through both lungs. To achieve this shot on a full broad side , you place your shot on the shoulder.
In my opinion, from all of my reading and research, a shot behind the shoulder on a buffalo can decrease your room for error, not increase it. A one lung shot buffalo is recipe for disaster. That said, anyone is open to correct me on my statements , I’m not an experienced buffalo hunter what so ever.