I've been trying to get a handle on this as well.
I leave my switch in the "A" position all the time.
Sometimes the little green indicator in the tach area lights up, even in broad daylight, sometimes it doesn't. It would seem odd to me that the headlights would be "on" in broad daylight. The dash lighting is usually not on when the green indicator is displayed. (I know this from driving into my parking garage at work.)
I'll have to get my butt out of the car and see what's going on with the headlights, I guess. Glad I'm not the only one confused.