National Federation Rules Free Throw Spaces

[Burtis449]

Can a legal pleyer "slide" down one space if that space is unoccupied by the player who should legally be there?

The player in the lane space nearest the shooter sees that the space down from him/her is vacant and just slides down there before the ball is put at the disposal of the free throw shooter. Not allowed in NCAA, but is it OK in National Federation? Rule 8 Article 3(F) is a little confusing.