As long as the position is of the same color the penalty is slim, besides the possession penalty, it's unnoticeable.
I think the performance penalty for that specific player is close to nil. The form is more related to that player's recent status.

Sometime ago there is a questionable tactic floating here, which is basically making OOP intentionally to get some possession penalty, so that the counterattacks become more effective.

I'd rather put an OOP player with good form into play than putting a bad form player who plays the position. The performance gap between good and bad form player is much greater.