The fact is that the closer to the sirloin a T-bone/Porterhouse is, the bigger/wider the fillet. That's a fact. I was a meat cutter for Winn Dixie way back in the day and we cut whole beef loins, not short loins, and their standard was the fillet had to be at least 2" wide from the bone to the bottom of the fillet in order to be called a Porterhouse. From just under 2" to 1", it was a T-bone. Less than 1", we boned it out and sold it as a NY Strip, even though everything above the bone on a beef short loin is considered a NY Strip. Another gauge is that extra seam in the strip part. It starts to disappear at about the same place that the fillet gets narrower than 2"A "true" Porterhouse steak is not just a T-bone with a large portion of tenderloin.