@vicvader77 Those are points changes not percentages. The percentage reported appears to be inconsistent (i.e. they don't actually reflect the rank change) so I have been recording my rank.
I have been playing with a friend and we always same increase or decrease in rank points from the matches. It appears that the points for a win or loss is shared equally among all players of a team.
How these points are calculated is still a mystery. How quickly you win does not appear to affect it (had one win where the other team didn't get to attack and we still only got about 4 points).
I suspect the rank change is some function of the "skill/rating of team A" vs the "skill/rating of team B". i.e. if you beat a good team you will get lots of points, but fewer if you beat a weaker team. Similarly losing against a weak team is worse that losing against a good team.
It could however be some function of team score (i.e. sum of individual scores) but sadly the EOR scoreboards don't persist long enough for me to track this i.e. if a player leaves at the end of a match they vanish from the score board. I suspect this is not the case however as very one-sided games do not appear to consistently score higher than balanced games.
With so many unranked players it is hard to get a match against a strong team unless they are a full premade in which case even one noob on our team will mean we're doomed!