I would not say it’s a universal feature of having noticeably wider soles on shorter irons. I quickly checked several of our current and they are either the same width or the short irons are slightly wider, like .010″ to .020″. That’s 10 to 20 thousandths of an inch. There may be some that are a little more, but not much. The front to back radius and sole angles will usually vary some. Remember the shorter irons are heavier and some of the very slight variance that I see or that we design is usually attributable to the weight. There are designs, and we have done them in the past, where the long irons are more offset and lower profile and have wider soles to promote lower center of gravities. This is for the purpose of helping players get those longer irons airborne easier. However, today most sets do not have a 2 or 3 iron because most are going to hybrids or utility irons that do have more of the wider sole features, for that purpose.
Your point of narrower soles in the longer irons making them harder to hit is not wrong, but sole width is not the only factor. It can make an iron less turf forgiving, but that depends on the turf. It can limit the amount of weight you put low, but it might not. There are other ways to move weight low. Still, we wouldn’t design a model where the long irons had a noticeably narrower sole width difference than the rest of the set, or a difference that would negatively effect the playability of the head.
Britt Lindsey