The mechanical form factor provides the bounds for the system implementation and dictates what size magnet or grade of magnet needs to be considered for the construction of your joystick or lever. Typically, Hall-effect sensors measure the magnetic field emanating from a permanent magnet. Unless the Hall-effect sensor is wired up with something similar to slip ring or is controlled from a local wireless module, the hall-effect sensor is most likely reside in the stationary part of the joystick, while the magnet is in one of the bodies that has some free range of motion. The magnet is some dimension smaller than that body. Consequently, for a subset of joysticks commonly called thumbsticks in gaming controllers, design is limited to a small magnet. Typically, only neodymium magnets are found in such a small form factor and these magnets are stronger, have greater temperature drift, and cost more.