Home location px4_home_lat vs / AirPort location nav_ah_lat

When starting … make px4 jmavsim
The simulated position is in Zürich …
According the docs is set home position

export PX4_HOME_LAT=28.452386
export PX4_HOME_LON=-13.867138
export PX4_HOME_ALT=28.5
make px4_sitl_default jmavsim

But in qgc there is an unchanged parameter for airfield home location 

What is difference px4_home_lat and nav_ah_lat in qgc and why use different parameters?