How clear is clear?

[Back In The Saddle]

In the closing minutes of a hotly contested game, A1 fouls B1 in the act, basket is missed. A1 earns himself a T disagreeing with the call. After the reporting, we clear the lane and shoot the foul, then the T. During three of the four free throws, members of A are moving in on the shooter, one player even going past the FTL extended. The obvious intent was to disconcert the shooter. I repeatedly ask the players to move back. A voice from the bench yells out, "they just have to be outside the 3 point line." I get more insistent and the players finally move back behind the shooter.

Years ago, I recall, we were encouraged/expected/required(?) to keep the non-shooters behind the half line. What is the current rule (Fed)? What is the best way to handle this situation?