Ekka, I watched nearly all of your vids and read most of your posts here and elsewhere about falling trees, so I have the opinion that you are a very skillful tree faller. I don't question for a moment that when you cut your scarf starting top or bottom you constantly check the cut matches the intended direction of the fall.
Like some of the others posting in this thread I was taught to make the initial cut from the top using the sighting line on the saw to aid accuracy in the intended direction of fall, I have cut scarfs the other way and all has been good, but for 95% of my falls the bottom horizontal cut goes in after the top angled cut. Using the sighting lines is something I do on the ground, in the tree with a top handled saw its not so simple.
On a not so different tack check out this forestry falling vid from Sweden its great.
Go to:
http://www.skogforsk.se/KunskapDirek...1362&bmp=11727
then: Film f?r bredband
then: Avverkning med motors?g (10 min) the bore is at about the 2:10 mark.
(other videos and info of interest are also there)
The raps for finding this one go to someone else, elsewhere.