Its best if the shoes don't make full contact with the drums. In fact they used to "cam grind" the new shoes so they make contact in or near the center. These old trucks didn't have an adjustable anchor pin. If the shoes were exactly the same arc as the drum they could make contact on the edges & pull or grab. After they wear in you will get full contact & a more firm pedal. You still get good brakes as the shoes flex to fill the drum unless like Long says if the drums were turned too far out.
