5 is meant to adjust the top part of the seat back rather than the head restraint itself, which is what I believe Robert adjusted to make things slightly better.
Looking on some of the US forums, seems the premium seats don't have movable headrests, other than the butterfly design which allows the sides to come in.
I guess the seatbacks with an adjustable top don't get forward/backwards adjustable headrests, and the non-premium seats do.