The setting number is irrelevant and will vary from grinder to grinder, antd here is no value whatsoever in shimming your grinder so as to make it dial in to any particular burr setting. It will vary dependent on whether Baratza put shims in at the time of manufacture (usually there's one in there), vary as the burrs season, vary with the coffee being ground and so on. As for choking your machine, if you can do this with your grinder you don't need shims. I suggest you should start to consider shimming when you can no longer choke your machine on the finest setting. You certainly need to add a shim when the dial must be set to or very near the finest setting to be able to pull proper espresso.