The two criteria is one; what can you safely get away with, and two; what do you need to make the arrows you are going to shoot fly correctly.
One; One similar bows I have made shelfs just over 3/4ths of an inch wide at the shelf..No I am not recommending it, but for competition archers shooting carbons I have cut past-center shelves which were thinner, but taller.
Two; This is what I usually do on a bow this style using wood arrows..I shoot the bow, and if the arrows I like go left then I will scrape the arrow pass in until they fly straight. If the arrows go right, you probably need stiffer arrows.
My "modern" looking one in the article is 13/16th's wide at the shelf for what its worth.. Ya the last place you want a bow to fail is in the shelf, that could be a bit nasty..
Rich