To answer your question, yes, bowyers do put their shelfs at different heights above center. They vary that much because bow builders place their arrow shelf anywhere from 1 1/4 to 2 inches above the center of the bow. Have been doing it that way forever. 1 1/4 -1 3/8 above center are the most common, but there are are quite a few examples of others as well. Add the 3/8 to 5/8 inch above the shelf that most people nock, and you get many of the distances reported.
For a string maker, it is a good idea to know how high above center the shelf is cut for optimal positioning of the serving. Guess I've been doing it for so long that I thought everyone knew about it.