Good question. I wonder what if any documentation exists. I always thought it was just an upshot of going for a fuller looking kilt with a better "swing". An evolution from belted plaid to philabeg to tailored 4-yard kilt, then just adding more material with deeper pleats for the look. More a case of tweaking a uniform for appearance instead of function.

While I think I still like my "tank" best, I must admit that the 4-yard box pleat is extremely comfortable, even in regimental wgt tartan.