Well, I had a chance to drive it at night, and my auto-dimming works after all - yey. (Sorry, I just got it & am still learning...) So, it's not just the headlights on/off, but - along with it - the sun sensor on dash also needs to know that it's dark out or not, it seems. (That's why the instrument panel doesn't dim even when I manually turned on the headlights during the day,. Pretty smart yet a bit confusing in an overly-automated way...)

So, I still don't know what the ECO Drive level & the dimming level that I've read about. I love how it says "Excellent!" (or not so) at the end, but I don't notice any dimming associated with it.