I can’t fully answer your question but discuss the importance of the front rank (file leader) and last rank (file closer).

In the ancient world, you traditionally want an experienced yet still active individual in the first rank. They’re the person who will have to do the fighting and have to be brave enough to stand and fight and not try to run. So ideally you want someone who’s a veteran and has (for some literally) ‘seen the elephant’. At the same time, they need to be young enough to be able to stand up to the rigors of physical combat. Also as a file leader they carry a minor leadership role in many armies.

For the last man in a file, the file closer, you want your second most experienced and steady hand. Panic in formations usually have their origin in the rear of formations triggered when men at the back feel the fight’s been lost and start drifting away. Their absence triggers a panic in the front ranks as they realize they’re no longer being supported and the fear spreads like a virus in a formation and every man is now concerned with escaping. It may have started with just a couple of men breaking ranks to the rear but suddenly the fear spreads and your entire unit is streaming to rear in panic. So you want a very reliable man at the rear to make make sure no one runs. You want a steady hand who will inspire or smack heads to make sure people stay in formation.

So you want your best fighters at the very front and the second best at the very back of the formation.