Centurion Position in Battle

[Nathan Ross]

One of his more significant oddities.

Yes it is! Unless we assume it was the same sixteen men all night, every night, there would be a constant carousel of tent-swapping going on... :-|

Any idea of the reason for the possible change (the bolded part of the quote) by the Imperial period?

Maybe the rise of longer terms of enlistment and the maintenance of 'standing' legions in the provinces, meaning that legions were not being so regularly demobilised and reenlisted? Also perhaps the rise in prestige of the centurion, meaning he could pick his own optio rather than being 'given' one by the tribune (and so therefore used the men in his own centuria)? But I have no great knowledge of the mid republican era!