basicially the more attacking you play the more players go foward sept for the defence, but if your playing attacking football then you will have to push your defenders up aswell to stop the opponents to expliot the gap between the midfield and defence
Just beware of too high a line because at the moment the ball over the top is far too effective (9.2) so you could be caught out even with Speedy Gonzalez and Roadrunner as your central defenders. Hopefully, this will be sorted out for 9.3 when it's released.