The depth of the bracket is greater than the depth of the front lip of the 16" shelf by this same manufacturer. The thinner shelf wire sits on the edge of the bracket whereas the thicker wire should set firmly on the bottom of the bracket. Notice the bracket picture shown for the fast track version, it appears that the thick slide rail rests firmly on the inside bottom of the bracket. I have the standard shelf (and standard bracket), and only a single thin shelf wire is supporting the shelf on the upper inside edge of the bracket. Perhaps the shelf lip width was shortened without doing the same for the bracket? Notching the bracket could make it work, but why is it designed so poorly to begin with?
BTW, package directions are also poor. They do not specify the relationship between the shelf height and the height of the holes for the rear or side brackets. They don't even mention the distance between the two anchors on the end bracket. Because the brackets are integral with the wall board anchors, the bracket cannot be pre-positioned to mark where the holes belong.