Re:
There is the technical manual in the Archive&Gallery, I think it's the last page of all the manual.
Bug bright M logo on the front page.
Should (maybe) help some more.
But 1 normally = least.
Best advice though.
Is set to 1, go ride your route.
Set to 6 ride it again.
Do that a few times, then guess were you would like it.
Ride again, tweak as you feel from there.
No doubt it'll change through time, but at least you know the effect it will have.
(Normally they say set it so the sag is about correct for the setting with you fully kitted on the bike, but try the fell first in my opinion)