The right-step is a feature and not a bug. It seems this is historically accurate - they actually did sidestep (to stay behind the shield of the guy to theis right in the phalanx). To solve keep two units - one in front of the gate and the other behind and to the right to "pick up the slack".

On the other hand it seems a bit silly, that the phalanx will eventually be facing the wall next to the gate rather than the gate itself...