Do wingers play a big role in Midfield ratings?

[Airhog]

or do they affect something else?

[Havok]

yes.... a winger with passable playmaking can help your possession and midfield rating alot!!!

i figured this out last weak when i played a back-up wingback as a winger and my midfield rating suffered

[lytic]

Not as much as an inner middie would... maybe 50%. It also helps the wing attack and defense.
However, most play offensive which helps more attack and a lot less defense and about 50% mid.
Defensive does the vice versa...
and Towards the Middle would do about 90% in the middle.

These are all guesses in numbers, but the theory is relatively true.