sleep tracking series 10

I have had my Series 10 for about 3 weeks and am struggling to believe what the sleep tracking is telling me. I thought that it tracked based on what you had set as sleep and wake times. Maybe I was wrong.

sleep tracking seems to start at some random point in the evening. I have my “bedtime” set to 11pm, yet sleep tracking will often start at 8 or 9pm ish recording time I know I am awake and, normally, watching TV as core sleep. As a result it overstates the amount of sleep I am getting by 1-3 hours.

Anyone any ideas why, or what can be done to improve things? At the Mekong the sleep tracking function is if virtually no value to me.