The Makedonian phalanx -- why such depth?

[Paullus Scipio]

Agreed...all the evidence, slim though it is, has been aired. Only once ( Xenophon) are we told what formation Hoplites customarily fought in - 4 deep- and only once do we hear of the depth of Alexander's phalanx in action - 8 deep ( Arrian). Elsewhere we hear of Hoplites 8 deep and sarissaphoroi 16 deep.The manuals tell us how the changes in depth were carried out - even to the fact that there were half-file leaders etc .....and evidently there is no viable alternative theory, at least that can be offered up here, to explain these changes in depth and their function.

We are therefore left with the model I have suggested or...............??????