Study this. Pop quiz tomorrow.
A real key to canti brake performance is maintaining the yoke angle of the straddle cable system. Most of the old canti brakes I see coming into the non-profit shop have an extremely acute angle at the straddle clamp, which I think comes from persistently tightening the brake cable to allow for pad wear, probably over many years and many pairs of shoes. I usually have to start from scratch, forget about the shoes, get the geometry of the calipers and straddle cable correct, then adjust shoes accordingly. Measurements depend on rim and brake boss widths.