Only the hoplite phalanx (and those similar to it) was known to drift to the right because of the effect of each man overlapping his shield with the man to his right. As far as I know the Macedonian style phalanx did not suffer from this problem.

As much as I hate to say it I would prefer to see the drift effect taken out of the game. Other than the fact that it's ahistorical to apply it to all phalanx capable units it's one more thing I have to worry about in an already busy battle environment and it does have an odd side effect which can cause a phalanx to contort itself in the weirdest way.