The Makedonian phalanx -- why such depth?

[Paralus]

[ Xenophon is perhaps our best source for much of this period- You'd prefer Ephorus??? He just has to be understood in context, and often we don't have the knowledge to do that since he leaves out so many details that are obvious to a man of his day.

He leaves out what is not conducive to his narative or his viewpoint. That, I'm afraid, is much.

Xenophon was well informed of what transpired at Leuktra -- of that you can rest well assured. What he chose to write is another thing.

Although Arrian in his tactical manual (9.5) refers to extending the phalanx by thinning, Plutarch's version is different. Lazenby hypothesised that in fact the 'folding back'( anastrophe) involved moving troops from the un-engaged left of the Spartan contingent to the right for this purpose, so that Cleombrotos was attempting what Agis at Mantinea attempted, and perhaps the Spartans were also trying to increase their depth.

I see nothing of that in Plutarch (Pelopidas, 23.1-2):

...the enemy understood what he was doing and began to change their formation; they were opening up their right wing and making an encircling movement, in order to surround Epaminondas and envelop him with their numbers.