Shield wall smashing through phalanx

Playing with BI and EB, i've noticed that quite a few of the units with shield wall can completely walk through (smash) my Elite African Phalanx (playing as Carthage), most recently its happened with the Elite Heavy infantry of the Italic Ages, they just go right through them, destroy the formation. Whereas i was under the impression that phalanxs are pretty much unstoppable when attacked from the front, and this particular unit of phalanx is very good. So anyways, Is this realistic, or should i try and change some formation settings or something

The phalanx have higher mass than other infantry. because of that they can keep their formation very well.
But unfortunately shield wall increase the mass of a troop and broken the balance.
maybe you can increase the mass of phalanx further more.