I usually play one centre midfield more attacking and one midfielder more defensive.... could that confuse the system thinking that they are more attacking than they really are. I even have one midfilder arrowed back so it doesn't seem to make sense.
What's the players mentality on the mentality slider. I think you want to try and keep the difference to about 5 notches difference max.
Having said that, you don't always need to worry about it, you might have to big a gap that can be exploited but it could work if teams aren't good enough to exploit it.