There are two currents used in motor calculations: FLA and FLC. One is found on the nameplate, the other from the charts in the NEC. One is used to determine the heater size, the other for determining the size of the conductors, the rating of the OC protection, the disconnect, and the controller.
The rational goes like this: The particular motor current draw will vary with the motor chosen and the load, but when you replace the motor, the branch circuit OC device, wires, disconnects and controller will remain. So the equipment and wiring are sized generically, but the OL heaters are fitted to the exact needs of the motor actually installed. If necessary, the fuse or CB is allowed to be bumped up to an even larger size if the motor chosen so warrants.