Eric, I didn't know the answer to your question, so I asked "Shotgun" and he sent me this. Hope it helps:

The Regiments Battle, Preparing to fight; "The Regiment drawn up for battle had it companies in the line two deep, numbered off from the right according to position in line, but given a letter according to the seniority in rank of the captain. The flank companies might be sent forward as skirmishers,; a color party of 9 n.c.o.s' was placed t the left of the 5th company, entrusted with both the safety of the color itself, and with marking the direction of the regiment's alignment by holding it aloft. The company officers stood as 'file closers" immediately to the rear of their commands: the regimental officers were further behind, with any musicians and the medical orderlies, chaplain and other staff."