Forgive me if I have missed this point if already covered. It was a quick read.
I have a question as a lowly SLF.
Some time ago I read that it is advisable to aim the fresh air vent to blow straight down your face so that all breaths are of clean filtered germ free air rather than regular cabin air full of nasties, and the air flowing down your face keeps cabin air away.
The article also said that the on board filters are extremely efficient and getting air direct from the nozzle is best.
But: is it not the case that this freshly filtered air may be clean of germs etc but is still a mixture of fresh and bleed air? So the theory won't hold up.
I hope you can understand that. Not one of my best. Thanks.