In my hundreds of dives with my spouse, I find that buddy position depends a lot on circumstances. Side-by-side worked when one was accepted as clearly dominant, like with this couple:
bisonduquebec:
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I am forcing my spouse to respect this rule and so far, she better enjoy her dive when doing side by side.
The dominant buddy points things out, asks for air readings, and is basically the guide and baby-sitter. When my spouse learned to dive, and maybe for the first hundred dives he did, we were side-by-side.
With more evenly-matched buddies in terms of accumulated experience (individual dive skills/comfort and as knowledge of the buddy), flanking or one-in-front (sometimes switching), seems to work out well. Buddy awareness increases, and we don't need to be glued together. The current procedure my spouse and I use for easy dives is most often like this couple's:
trigfunctions:
<snip>We have found it better to be far enough apart that it is easy to scan and find the other - about 10 or so - but close enough to react if help is needed.
But, if there's a significant current, or if viz is poor, we try to stick closer together, ususally single file for current (to stay close to the wall or bottom on the same path) and side-by-side for low viz (to reach out and touch).
Sometimes in low viz we will get out of sight of one another, though, by a few feet--usually a consequence of one or the other of us stopping to take a picture. I'm always aware of where my buddy was heading when I stop for that shot, and one strong fin kick brings us together again.