The Makedonian phalanx -- why such depth?

[Paullus Scipio]

Paralus wrote:

Again, you make far too much of the very scant evidence.

....well, the evidence is 'scant' for any aspect of Greek or Roman Military history, with many'gaps' and unknown mysteries, and a great deal of history of which we know absolutely nothing.
Here too, the evidence is 'scant' I'll grant you, if taken in isolation.
However, when put together and a 'holistic' approach applied, a consistent picture emerges.

For instance...

Do they tell us this for the army under discussion? The army of Issos? Do we have any clear statement naming half file leaders in Alexander's phalanx? And, if there were "half" file leaders does that not indicate that the usual was "full file" (that is, 16)?

That is a sophist's trick to attempt isolate an argument. I am speaking of Greek/Hellenistic drill generally and the idea that depths are quoted by most ancient authors for troops in 'normal' order, and that this halved into 'close' order before contact. If we are not specifically told of 'half-file leaders' in Alexander's army ( and I haven't carried out an exhaustive search), we certainly know that 'half' and 'quarter' file leaders existed in Xenophon's time, and that 'Dilochites'(double file leaders) also existed in both Xenophon's time and that of the Manuals.... we may therefore assume continuity as highly likely.
And yes, the 'normal' file usually stood 16 deep, except when going into action, as I have described. That's the point. The file 'normally' stood 16 deep, and only closed up for action. For all other purposes it stood in 'normal' ( open) order.....
Further, in Arrian's version, he specifically tells us he is drawing on a number of Greek Tactical manuals -Clearchus,Pausanias, Evangelus,Empolemus and Iphicrates (not the famous Athenian), Polybius and Poseidonius of Rhodes. He refers to Hoplite equipment as well as Macedonian, and states categorically that he has "given an account of the old Greek and Macedonian formations..."
That being so, and a continuity seen from Xenophon down to the Hellenistic Manuals, it would be a brave scholar who would say "except in Alexander's army", especially when what we are given - scant though it may be - is consistent with all the other evidence. ( How could Alexander's phalanx get down to 'half-files ' of 8 at Issos, which we are told they did, if there were no 'half-file leaders?)

As to the silly statement of the "others" being reduced to "spectators", your own preferred source (Polybios) clearly explains what they add to a phalanx "when sixteen deep".

The statement is not "silly" at all. Many learned military commentators down the centuries have been concerned that such a formation is really far too deep to be effective or practical. And Polybius' statement is just as consistent, not to mention more logical, when the file of 16 he refers to closes up to 8 just before contact, for then the back 3 ranks " add their weight" to the front 5. ( it being appreciated that this "adding weight" can only occur when the two respective front ranks are in contact, fighting, and perhaps shoving if we take the term literally). The idea of 11 men, though, leaning against the front 5.......

I notice you studiously avoid answering my question of just what the half and quarter file leaders are for.....nor do I see any attempt to come up with an alternative explanation which fits our 'scanty' knowledge better, or is consistent with ALL the known facts......