MPF is only related to the mass and dimensional characteristics of the club head. Ralph explains completely in the original book on MPF that the MPF does NOT consider the fit, shaft, grip, etc. in a golf club. The head is a free moving object at impact operating on it’s own mass and dimensional characteristics. The MPF gives us a tool to define a head designs stability based on it’s CG location in multiple planes and it’s overall mass distribution. These factors determine the “Playability” of the design. If you have a low playability design and are fit perfectly, and if you are a good ball striker, the club should perform well. The same goes for a high playability design, with a good fit. However, the higher playability design will perform better on mishits, big or small, providing more consistent distance and dispersion. If you have a club that is not fit well for you, if the head is a higher playability, it will perform better than a low playability design that is not fit to you. You have to look at the iron head design as a separate component of the overall playability of the design, just like you look at the shaft and grip as separate components. Having all three fit to your unique swing is what all players should have. That being said, the head is the only component that strikes the ball and we want that component to have the best mass and dimensional characteristics possible so the result is optimized, no matter where you strike the ball on the face. Again, if you strike every shot dead center (assuming the cg is dead center), the playability rating of the head doesn’t matter as much.