El demento idea here (been up most of the night with crying baby syndrome, so I might not make much sense today)
What if one of the 3v3 missions used a map that effectively turned it into 3 seperate 1v1 battles? Player A from team 1 faces player A from team 2, then a big distance away from them B is pitted against B, and a big distance further along C is pitted against C.
The theory being that the attackers split up along three different paths, and the defenders couldn't let one of them slip through unopposed while they focused on the others, so the defenders split up as well.
It's not something I'd want to see frequently, but could be interesting
dave