Up to today for making pate brisee/sucree I always used KA AP or a blend of KA AP and White Lily (WL) AP flours and my shells always shrank while baking - even after allowing the shells to rest in the freezer for a couple of hours once they were rolled out. So today I followed Ruhlman's recipe to the letter using the 3:2:1 ratio but also using a mixture of AP and pastry flour. What a difference the pastry flour makes. Once baked I noticed that the shell conformed to the exact shape of the tart mold without any shrinkage and without any bulging in the well of the shell. So the idea is to use a blend of flours to include pastry flour; it'll result in a lower gluten content than only if AP is used.