New Fenix 6 won't track sleep and baffling power save UI seems to opposite of what should happen...?

Hi

I got another Fenix 6 a day or so back and found this one simply fails to track sleep (or any sleep metrics)

So I use power saving mode during sleep (10PM to 730AM) so first thing I checked was that the WHR wasn't being disabled overnight - it's not...

but..the UI here makes no sense!

Two options (don't change / turn off) - you'd think if Don't Change was selected which means On on this case, you'd lose battery power, but no - I GAIN 8 days battery apparently!

And I double checked this screen on the other Fenix 6, and this shows the same thing - Turn Off WHR shows 8 days battery loss, whereas turning it off overnight should INCREASE battery life, not have a negative impact on it.

Obviously this should be the other way round

I still can't figure out why the new model won't track sleep - or am I completely misunderstanding the UI here?

Either I have gone insane, or the UI is showing the exact opposite of the expected behaviour - in that turning off WHR should save power....?