I also wish this was selectable. It sort of can be done but it would be quite cumbersome on the design/assembly and the way things are. Something that some of us do is code the dim mode so it only comes on after sunset. By day the face just darkens a little as defined by the hardware I guess. For me this solution has renewed my enthusiasm for including a lume in the design.
If you will check the settings on the Facer watch app at the end of the âwatch boxâ is a settings panel that has the option to do exactly what you want in dim mode.
Just set the AOD setting to âDimmedâ not âClassicâ like I have mine. That will have your watch just dim the active face and use that for AOD mode. Setting it to âClassicâ like I have mine will use the dim face the author programmed for their face.
I also noticed I need to clean the screen on my watch. I hadnât noticed it until I saw the picture I took of it. 
That is apparently only a Samsung/Tizen option, that isnât available on WearOS watches 
Yes, sadly I just checked my TicWatch E test watch and itâs Facer settings screen only has options for 12/24 and imperial/metric.