When Ralph developed the MPF, he did a lot of measuring of complete sets to see how the mass and dimensional characteristics and the variation by loft would effect the playability. Generally, there are slight variations in CG locations both vertically (.005″ to .015″) and rearwardly (.010 to .035). Also, it is important to note that the more loft you have the more oblique the hit, or the less direct the impact is. The more loft, the less the horizontal stability (or MOI) will effect the result. It’s still important, but not as much as on the lower lofted clubs. So, in short, the slight variations in cg location throughout the set and the slight variations in the type of impact and point of impact are not enough and do not translate into playability factor variations within most sets. I suppose there is a possibility that some type of design could do something radical in the progression of each iron within a set that might cause the playability rating to change, but we have not seen anything like that to date.