What I have noticed from my experience the past few seasons is that sometimes form is a much more important factor for the performance of the whole team.
As well, another observation I made is what kind of formation and tactics/orders u are using. I changed my strategy from a more containing way to a full hard attacking type of play and noticed that the form of some players have increased suddenly. Here is an example :
Here is the list of few players performance after the change of the strategy used for the last 2 days
Note that Guajardo has played the 2 last games, the first for 90' and scored 4 goals and the second for 30' and 1 goal scored.
Rauch(1G), Rangel(2G),Anom(1G) and Hoie(1G) played only the last game.
My conclusion about this is that the type of mentality combined with the orders used in every game can affect the form of your players.