Think the shapes have altered over the generations, impacting upon the performance.
Didn't like SM5 - thought them a bit square and difficult to vary the face angles.
SM6 were OK, more rounded, but I struggled to find consistent control over them.
SM7 seem to be slightly different in shape but I love them to bits. I can open the face and feel in control of my shots and have greater confidence with them as a result. This confidence continues to build, feeding itself and as a consequence, my short game is as good as it's ever been.
Not convinced they are getting smaller, just changing shape.
JT

I thought the same thing this weekend; I picked up an SM7 in the store and thought, wow the head is more compact. It certainly could be the shape altering the look. Either way, I love it.

They have a few things going on as each generation progresses....first, cosmetics; second, grind availability (SM7's introduced D grind for instance); lastly, the launch angle is more controlled with the current generation of wedges so that shots do not balloon. As far as the size it is a function of the shapes. More people prefer wedges with rounded angles versus straight so the wedges appear to be smaller. I have not heard recently of any significant size change however shape is changing constantly depending on preferences on tour and the marketplace.

I've played all 3. SM5 48-08, 54-10S and 60-04L. Initially started on SM6 50-08, 58-12K (bent to 56) and 62-08M. At this point I have SM6 46-08 (bent to 44) and 50-08, and SM7 56-08M and 62-08M. SM5 54-10S was great for chipping and pitching but not so good out of bunkers. The SM6 62-08M hits better in a hard bunker vs SM5 60-04L. The 58-12K was great out of sand but not so great around the greens. The SM7 56-08M and 62-08M are versatile.

I have the 48 54 58 f f k grinds all sm6 model I like these the best of all