I would be interested to understand how much the ball possession might affect the match result in case of opponent of the same level...I mean I have lost matches with more that 70% of ball possesions (due a big amount of friend and manager on the bench) against opponent of my level...

I think it is right that the attendance of friends should not affect highly the match result...but indeed it is not correct to reflect the friend attendance in a bonus in ball possesion...maybe it could be better to affect (even with an hidden parameter) the average team morale