I have been in the (pleasant) situation of fighting against enemies with my long pike phalanxes where the enemy flee from the flanks but there are a couple of tough units still fighting in the centre. Does anyone know how you can order the phalanxes on the flanks to press forward against the sides of the enemy? I find that if I realign the flanking phalanxes to attack the sides with the usual guard/phalanx mode enabled the phalanx will kill one or two enemies from the side, then will no longer be engaged with the enemy.

Is there any way of making sure that they continue to surge forward as enemies are killed (without doing anything stupid like switching to secondary weapons etc)?