rear-facing

Tesla encourages the use of the fresh air setting for better air circulation when using the rear jumpseats. Can anyone explain why that setting has better circulation to the trunk? When I put that setting on, the speed of air exiting the rear vents noticibly decreases.

I know it looks silly but does anyone have experience with the Noggle in the Model S? I have 3rd row jumpseats and wanted to hear from anyone that's used one before either with that or with rear-facing car seats. Specially, what length is appropriate and how well does it fit on the rear vents?