I'm fairly familiar with how pickups work (difference between single coil and humbucker, coil splits, coil taps, active vs. passive, the fact that they are made from magnets with wire wrapped around them, etc.), but the connection between build configuration and the resulting frequency response is still a big mystery to me.
Suppose that a manufacturer of passive guitar pickups has an idea for how a pickup should sound, how would they go about achieving that sound? How much fine tuning is possible? Or maybe they go the other way: make many combinations of magnet type X magnet strength X amount of wire, and then categorize the results?