Seems to me that there are two settings....Adjust it during daylight operation to set that one and then once it is in night mode adjust that one to your preference.
Do note though that there are multiple sensors. One turns the auto headlamps on and off and the second one controls the dash lighting. Thus in some circumstances, such as a rainy / snowy day, your headlamps may turn on yet the dash lighting remains bright until / unles the cabin is dark enough for that to go into night mode as well.
Once set they should remember the correct setting.....
My 2017 Ultimate does the same thing and I have been trying a few different solutions, my 2013, 2014, and 2015 did not do this. A new cluster did not fix it and I have now ordered a new dimmer switch. I will let you know what fixes it.
I do not like the way it works either (2017 SFS, Premium pkg). It seems to have a mind of its' own.
I should be able to turn the headlights on and adjust the brightness of the three instrument displays, but it doesn't work that way. May times the left and right displays may dim but the center is bright. Sometimes they are all bright - I have the illumination turned down to the minimum.
One thing I did notice - If I cover the sensor at the center of the dashboard, under the windshield the display will dim. I threw a glove on the dash and discovered this happens.
No one seems to have an answer how this works, other than the owners manual information.
It is a nice vehicle, but things like this make me wish I still had the 1998 Explorer.
As I mentioned earlier, turning on the headlamps will not dim the display unless the interior or wherever the sensor is located is dark enough to dim the display. Why is it done that way? Some people drive with their headlamps on all of the time. Vehicles operated by the emergency services may do so as well. On heavily clouded days the headlamps may turn on and if the dash dims all of the time it may be difficult if not impossible to see. Ditto for people who drive in parades, funeral processions, etc..... Personally, I like Hyundai's way of handling dash illumination.
With our other product line.....Every years we have dozens of people who come in saying that their radio display goes dark at random. The cause is....You guessed it....Since the radio dims anytime the headlamps go on it goes dark on very cloudy days and unlike the more intelligent people here, they see it going dark as a problem and schedule it for repairs.....
I do absolutely agree that the owner's manual does a poor job of explaining how the headlamp and dash dimming systems operate.