With the lights set to Auto, they will dim out completely with headlights on, If you select Day, with the Night set to 10, the will still dim with headlights, but will remain brighter. Auto seems to be a Dimming level, not a selecting of automatically dimming.
So adjust your Night dimming level, and leave the selection on Day, and turn your headlights on and off, you will see the difference compared to Auto.