know this will probably sound stupid but, what SPEED do you have your game set on?
Playing as Scarborough, I got got to the new year with three of my stikers scoring all but 2 of the teams total goals (the other 2 were a free kick & penalty from a midfielder). This was on Medium speed and Extended highlights.
For some reason I decided to change the game speed to Very Slow and suddenley my midfielders all started banging goals in. In seven games runnning on V.S. I had 13 goals - 5 from forwards, 7 from midfielders and 1 from a defender. The midfielders also seemed to have more shooting opportunities over this.
No doubt this is just a coincidence but maybe it's worth a try changing the game speed and seeing if that makes any difference (running at a slower speed might give the computer a little more time to do it's calculations and end up with placing the midfielders in a slightly better position - as I said, sounds stupid!).
Of course player instructions will play a big parts as well. Pushing the midfielders forward and telling them to make forwards runs should get them into better positions.