Alright... well I just finished a cup match and lost 2-1, but losing isn't a problem, it was the way in which I lost. For example, the opposition had a slightly weaker team which consisted of 14.3 stars (on average) against my 14.7 (on average). A close match you would expect? That's exactly what I would've imagined until I noticed that all of his players were out of position! His goalkeeper made an appearance in defence, his midfielder was playing in goal and his defender upfront! There was only 5 players playing in their correct position, and with me spectating and playing at home (+13% possession bonus) I thought a win was on the cards. I went 1-0 down to which I responded by copying his tactics and ended up having 69% possession and losing 2-1.
So the real question is; does it matter what position your players play (do you get given a deduction in stats) and what are the best chances of winning?