I usually have to data sources in my sleep data:
  • from my iPhone (based on the set focus)
  • from my Apple Watch (based on my movements)
The time in bed seams to be correctly calculated from the Apple Watch source, the shown time duration (e.g. 23:44 - 07:01) uses all available data sources. Also the time to fall asleep is calculated based on all data sources.
Does numbers should only be based on the Apple Watch data, if this data source is available. Only if it’s not available, it should consider the iPhone as data source.