You can have more than 2 wingers. Example the 3-2W-2N-2W-1 (Butterfly) formation. The possesion difference is only accounting for the spectators & because I was playing force counter-attack tactics. Still doesn't reach that 20% penalty.
Click image for larger version. 

Name:	T11-butterfly formation 1.jpg 
Views:	46 
Size:	95.1 KB 
ID:	7681Click image for larger version. 

Name:	T11-butterfly formation2.jpg 
Views:	39 
Size:	94.9 KB 
ID:	7682Click image for larger version. 

Name:	T11-butterfly formation 3.jpg 
Views:	35 
Size:	94.9 KB 
ID:	7683