My dear friend HBDiveGirl summed it up, a long time ago: Dive to stay found. No matter what the conditions are, or the formation you have chosen, it is incumbent on all of the divers in a team to remain mindful of the need to keep the team together. If nobody takes off in an unpredictable or unplanned way, almost any formation will work. I am reminded of a day a year or so ago, when I went out on a charter boat with a fellow photographer friend. Kathryn and I had a fairly general dive plan, to follow some terrain the captain had described, but obviously, we were typical photographers, and could be distracted quite out of the planned route if something interesting presented itself to be shot. I'm not even sure we HAD a formation, except during the periods where we were actually swimming and covering ground. The rest of the time, one of us would find something to shoot, and the other would cast around in the vicinity for something else. Each of us was aware of the firing of the other's strobes, even though we might at times have our backs to one another. When we finished our set of shots, or when the other person's strobes ceased, we would look up and make eye contact, and if it was clear that that particular area was done, we would move off together.
It worked, because neither of us was going to leave without checking in with the other.
While covering ground, though, we stayed roughly shoulder-to-shoulder, with the lights swooping back and forth in front of us, where both of us could see them.
It's actually fairly difficult to describe how it works to someone who hasn't dived this way, but once you have developed awareness of where you can be seen and where you can't (and the behind and shallower, or "death from above" position is horrible!), and you have placed team cohesion as a priority, it really isn't very difficult. Storker, if your buddy is diving DFA, he probably doesn't realize that he's invisible in that position, because he sure can see YOU. Either that or he may, as my husband does, stubbornly maintain that he is NOT either above you. Peter didn't admit that until a tech instructor had us all wear Sensus Pros, and he plotting our positions and showed us where we were. Peter was consistently about 3 feet above the rest of us. He just honestly didn't believe it.