I can find no reference to how far onto the court the "coach's box" is. 38 feet from the end line. "Recommended" that a line 2 inches wide by 3 feet long marks the end of the team bench area. But I can find nothing that states the coach's box is actually limited to 3 feet.
This might be old (but it includes 2017/18 rule changes)--
This might be old (but it includes 2017/18 rule changes)--