Tio wroteYes, it is a violation if the first marked lane space (the very first spot is always unoccupied now) is not occupied by the opponent of the shooter.
Don't think 10.1.5C agrees with you. It's not a violation. It's a T, if merited.
10.1.5C: "...(after a foul is reported)...(b) two B players are not occupying the first two marked spaces next to the end line as required. RULING: ... In (b), Team B will be directed to occupy the required spaces. If there is a delay, a team technical foul shall be charged to team B."
I blew this two years ago by giving a DoG warning instead of a T when the coach insisted on keeping his five players by him near his bench while we were preparing for the opposing team to shoot free throws on the other end.