Would a mob formation of 20 be deployed as 4 ranks and 5 files or 5 ranks and 4 files or whichever suits?

When casualties are removed, do you remove strictly from the back rank or back and sides to keep the formation as close to even ranks and files as possible?

After combat does the formation automatically re-order to even up ranks and files or stay as-is after losses and any wrappers go back to their previous place?

5 ranks and 4 files; always build a square, and put any extras in back.

Casualties come off the back then sides, keeping it in a square shape as much as possible.

After combat it automatically goes back into the original mob shape.