As I have said before, the battery usage estimation in Android is never spot on with reality and this is particularly true with ZenFone 6. To be honest, it has flaws, we know about them and they will be fixed in Android Q. It's still not going to be perfect because it's not perfect on any phone but it will be a lot better.
The best way to know if there's something wrong with your phones battery is to put it in flight mode when you go to bed without plugging in your charger. If you phone doesn't loose more than 1% of battery per hour of sleep, then there's nothing wrong. If it's more than that, then we can investigate why your battery drains faster than it should.
