My preferences are...
Use a dark theme.
Use a dark wallpaper.
Use Dark Mode.
I don't use adaptive brightness.
I turn off the battery % sign in my status bar and just enjoy the phone. 
If your signal isn't the best then your phone can work harder to maintain connection causing increased battery usage.
Battery life i.e screen on time is a very subjective topic as we all use our phones differently, use different apps and have the app preferences set up differently and network signals are different.
Your phone will take a short time to learn your usage habits and should then optimise things for you.
Also your battery won't hit optimal levels until it's been discharged and charged a few times.
Of course a person uses more battery in the early stages of owning a phone via setting it up and using it more to set it up and learn any new features etc.
If you perform a search on this forum and via google you'll come across other tips such as location accuracy settings etc and more.
