Centurion Position in Battle

[Nathan Ross]

Vegetius' century is 111 including the centurion, or 100 + 10 (file/contubernium leader/decanus) + 1... He makes his turmae also larger at 30 + 3.

Wow, this is really interesting! Can you please provide exact sources that say this?

It's Vegetius II.14. But the turma is 32+1:

...habet una turma equites XXXII. Huic qui praeest decurio nominatur. Centum enim decem pedites ab uno centurione sub uno uexillo gubernantur; similiter XXXII equites ab uno decurione sub uno uexillo reguntur.

One turma contains 32 cavalrymen. The man in charge is called a decurion. As 110 infantrymen are controlled by one centurion under one ensign, so 32 cavalrymen are governed by one decurion under one ensign. (Vegetius, II.14, trans. Milner)

The extra ten men in the infantry century are the decani, or heads of contubernia, which Vegetius says have ten men each. There's no specific mention of them being 'file leaders', although V does seem to think the contubernia 'fought in groups' and used to be called 'maniples', whatever that's worth...