Where should hardcoded variables typically be stored in FLASH on a microcontroller?
Some micro-controllers have protected areas, which require additional steps to program and erase. Calibration parameters are usually stored in such areas, as they usually survive a firmware update.
Other micro-controllers have areas of the flash that behave as EEPROM (single byte erase instead of sector erase). Parameters can be stored in such areas.
If neither option is available to you, where ever is convenient is OK, as long as the programmer that comes after you knows the convention.