TSandM:
... defining a crisp formation works very well if you are diving the top of a wreck, or marching from one place to another. But when you are cruising the top of a reef, nobody wants to dive in lockstep. I sure don't... To dive a team of three on the top of a rich and interesting reef requires that you define acceptable separation...
Through experience, we have found that,
for us, using either the delta or echelon arrangement
while in transit, especially at a good pace, is effective in minimizing buddy separation (by the way, we typically only have 10-15 foot viz) and ensuring quick seeing and responding to a buddy issue, if needed. We have also found that once at a point of interest, typically a reef, then positioning is typically not an issue, as long as we stay within preset distance and can see one another without having to twist/contort our bodies or turn our heads completely around (required if all 3 of us are in front-back, straight line, single file - which we have found to be very annoying and troublesome). So yes, to us, we have found that it's more than just acceptable separation distance. It also means avoiding certain relative positioning (usually just one specific) that creates blind spots, diminish the fun/joy (because of having to turnaround to look, etc.), reduces the likelihood to spot buddy issues, etc.
I've had my share of errors in trio diving, and I've learned from them. They have also made me a more conservative diver. Sometimes we do dive in lockstep over a rich reef, especially in poor viz, so it's
not true that nobody does that. We have found what works for us and for our level of comfort and experience. We are keen that it may not work for all, but then some other method/style may not work for us either. That's why we say "what works for us" and what is "to be avoided" and
not "best buddy positioning for 3 divers" or "worst buddy formation." To say anything in absolute terms or authorative manner would mean that we know everything about diving... we do NOT... and have not seen anyone who does.