Difference between stages and amounts sleep tracking average time asleep

I have been tracking my sleep with a Garmin and sharing the data with Apple health. In January I switched to an Apple Watch and continued to track sleep. I was checking my 6 month trends and noticed there’s a large difference between the average time in bed and the average time asleep on the stages VS amounts view.

os there a difference between these? Shouldn’t these be the same figures? It’s the same looking at month down for averages but when you switch to 6M the numbers change massively. Why is that?

attached images for reference: