I'm happy it helped you! I do find it hard to understand what exactly you want me to explain more about, and also text is a crappy medium to explain things that should be explained visually :( I'll try..
The formation rectangle is more of a result, than an actual 'object'. For example, the striker might be at coords (1, 0) in the formation setup: the most forward position, and in the middle. But during a match, they're only there while their team is attacking, and the ball is close to the opponent goal. While defending, this player might end up at (-0.5, 0) - halfway it's own half (but still the most forward of their team).
So, the original formation might have players positioned from (-1, -1) to (1, 1), but during a game, this rectangle is compressed. For example at the start of a match, both teams are on their own halves, so the players of team 1 would be between (-1, -1) to (1, 0), which you could visually see as the formation rectangle being compressed in the 'depth' axis. then as the ball moves forward, this rectangle moves up.
Again, this is not an actual rectangle, but just a result of the player's positions moving up and down with the action, while still retaining the formation's 'form'.
I hope this helps.. (but it could also be that you already understand this, but have a problem with translating this to actual code/math?)