When using the sling system on my No.4 T always 1/2 a turn to the left (Anticlockwise) then put your arm through the loop tighten it down then fold the sling as above behind your wrist.
The half twist allows it to lay flat against your wrist as otherwise its trying to fight you, wont lay flat usually get the edge and not very comfortable at all.
Lefties do the opposite. Speaking from experience.
I've always wondered how soldiers had the time to unship the lower link and form the regulation sling. I wonder how often a hasty sling was used instead.
Bob
"It is said, 'Go not to the elves for counsel for they will say both no and yes.' "
Frodo Baggins to Gildor Inglorion, The Fellowship of the Ring