Line relief using open order file gaps is rubbish. Here's why....

[Justin Swanton]

Does no one describe the legion in action and how it deployed that may provide further clues?

Oh, the sources describe it, enough that we can know, but the quincunx has been part of established academic conviction for too long. Almost impossible to get anyone to consider that it might be wrong. I think that it will eventually shift but somehow I can't be bothered to make a lifelong crusade out of it.

[Monad]

However, I don't think you are right on the subject of testing back to basics.  It can work in a very tight subject area but you cannot apply the same detail across a wider range of subjects.

Have the re-enactment societies tried practicing line relief? If so I would like to know what their conclusions are.

It is not clear to me that the Romans had a formation called a quincunx or even that the word always meant what we use it to mean today.

Aulus Gellius (10 9) mentions a military formation called Serra (saw), which I believe would be more appropriate than quincunx. Vegetius (3 19), describes the Serra as the name of a formation which is ranged by crack troops before the front, facing the enemy, so that a disordered line may be repaired. Festus (466 28L): "To fight in saw-formation is said when there is a constant advancing and withdrawing, and no standing still at any time."