sleep coach needs help with basic math

Why doesn't Garmin fix the sleep coach.  

I sleep over 8 hours, get a "fair" score.  Sleep coach says I need 7 hours 50 min and adds "You could use more sleep".

Doesn't Garmin realize how inept their software is?  

Why not let me set the sleep target and evaluate my sleep based on that. 

What is the value of sleep coach??