The Makedonian phalanx -- why such depth?

[PMBardunias]

Here is what he had to say about forming synaspismos:-
"Doubling the files proved far easier than expected. Formed up in the two-cubit formation (close order/pyknosis) with pikes in the upright position....[the file] ...came up the interval between the other two files. They then levelled their pikes proving it was possible to 'double' the formation allowing only one cubit per man".

Note that they have to raise their sarissa. This is a problem for Aelian's doubling by moving every other man in the file forward and support for doubling by half-files. The rear half of the file already have sarissa sloped, though with enough time anything could be done.