It's called string follow because the string is the force that applies the set. I'm not sure why this degree of something is so hard to grasp.
I've often said that nobody but the builder knows the original profile of the stave so why so much agonizing over what to call it?
Technically I would say that from an original profile of 4 inches of reflex, your stave has followed the string to 2 inches of set from the original profile.
So it has either 2 inches of string follow or 2 inches of set, because they are the same thing.
Remember you're giving all the data. If you just handed someone a shot in stave with 2 inches of reflex they wouldn't be able to even discuss it's degree of set/string follow, even though it is hidden in there.