Up until FIFA 14, you were able to customize your formation positioning and move players around on the pitch. If you moved them too much though, their default position would change along with the formation -- with 442 for example, if you moved a LM forward further than a certain predefined point, he switched to a LW and the formation changed to 433. Positioning was also restricted, your DF line for example couldn't be moved any further than half way up your end of the pitch. I removed the predefined borders which allowed players to be moved anywhere with no changes to default position or formation.
That feature isn't in the game anymore (that I have seen), but I'm still able to accomplish the same thing using my table plus applying edits the formation table. Adjusting player positioning in this way does impact how far up/down the pitch players will station themselves. I create several custom formations and switch according to game situation. I create one formation where I position all players in my half of the pitch when I wish to play park the bus. And I create an all-out attack formation and position players on the CPU's side, I use that formation when it's late and I need a goal.