Until now, I still don't get why training alone (against a wall) in passing trains faster than training in tandem
It's not with a wall. Single position you throw the ball to a coach, who tells you what you did right or wrong and you get the next ball from the rack. Two position means you throw the ball to a teammate, who tells you what you did right or wrong, and then wait for him to throw it back and tell him what he did right or wrong. Anything you can do, two can do slower! ;)