The Makedonian phalanx -- why such depth?

[Paralus]

Eee...rr...rrr.... No, in fact. The sources would have it rather differently, with the caveat that all is open to "interpretation"....

You'll have to quote me the passage that states that Eumenes fielded more "heavy" phalanx infantry than Antigonus. Diodorus is alarmingly clear on this point. And, before the issue of "interpretation" is raised to colour matters, remember we are dealing with a "satrapal" coalition of the "upper" satrapies: the cypher for that interpretation. Peucestas, alone, is noted as adding a further 10,000 "bowmen" from Persia. Although Eumenes' army numbered "36,700 at this time" the vast majority of of that ilk. The only attested "heavy" phalanx infantry number 17,000. This accords well with the 13,000 odd he left Cilicia with.

I doubt he stood Persian bowmen and other such in the pahalanx line to simply fill out some.