spartan army at Mantinea 418 BC

[hoplite14gr]

So ok,the Perioikoi had become part of the enomotia...
And if indeed more than the half enomotia was consisted of perioikoi,it makes sence if the front two ranks were homoioi and the ouragoi were also homoioi,keeping the perioikoi packed between them.
Khairete
Giannis

That was the way it was done and it was not a Spartan novelty.

Homer describes Agamemnon masralling his troops putting forward the bravest, to the rear the steadiest and the "bad ones" in the middle so that even the unwilling would be forced to fight. And we all know that Homer was akin to the "Holy scriptures" for the ancient Greeks.
As for the Spartan unit structure you might have read our article last year about the Spartan Army in the magazine.

Kind regards