SOT is only one measure of battery life, the battery still depletes when the screen is off, especially if you're doing something like listening to music for 7 hours......
If you saw the YouTube 'battery drain' tests, the majority are in a room, mobile turned off and on WIFI. They are in constant use with minimal ramping/up down of the processor as they only switch apps every hour. These guys achieve up to 9 hours with constant use in optimal conditions.
If you extrapolate out your current usage you're on for 7 hours with 51 hours total, which is very very strong. People would kill for that endurance
At best you can expect 0.5% an hour drain if you aren't using the phone, but that's if you literally leave it overnight and don't touch it. More likely it'll be between 1-2% depending on usage, so if you calculate you've had roughly 10 hours of screen off, that's about 10% battery that isn't being used on screen on time, which equates to roughly an hour of SOT 'missed out on' if you were just to run the device with the screen on for the sake of it.
If you're truly only concerned about SOT, run a day without music in the background and see the improvement. It's a nonsensical thing to do as that's not how you use your phone, but will get you the numbers you want...
You're also using a high end processor and a large screen with a high refresh rate, it's going to use more juice than a mid range or low end phone. If you send that phone back, someone else is going to be very happy when they get it as their replacement