Can control fields be formed with more than three portals?

I keep answering my own questions. After work I made the walk to E and linked A from there; it formed a closed polygon but failed to form a control field. Just closing the shape isn't enough, it must be a triangle formed from three links and three portals.

D wasn't actually that far from E, and there was a random key for B lying on the road between A and E, so I linked what all I could and recovered part of the area we had before, mostly the outer edges so the enemy can't block us from finishing our links (at least, without just blowing up the portals again :D ). Only problem is that my owned portal - A - is now being used as the main lynchpin, and it's weak (I just hit level 3 today), so we're likely to lose these fields again, but hey, more AP for me.

Don't forget using the fields to form layers! If you layer it up you'll have a strong protection for the inner portal control. Around here we've battled back and forth, and at one point there was a nine layer "cake" of fields that the opposing faction let stand for a few days due to the complexity of trying to take the network down.