I ignore all and any infantry when using the scythed chariots - the true value of the chariots is absolutely massacring cavalry (especially the successor and cataphract types of the east). Use them for that and stay away from all infantry - any infantry, even the weakest kind will mess up up the chariots.
Presumably, you run the chariots in right angles to the phalanxes - though I havn't tried it.
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