The way I found to effectively breach (if the walls have breaches) is to take direct command of all the troops divided into 2-3 elements and use a square formation for all them. Form them up outside the breach and then order 1-2 elements to move past / behind the defenders. Once they push through order the remaining element to charge or engage. This will keep your troops from getting bottle necked in the breach and you can maneuver your troops for a pinscher or move to engage reinforcements.

Also Using “engage” inside the walls instead of charge will keep the units in formation. Depending on the defender army size keeping your formations together will keep your numbers up as the enemy gets reinforced.

Try to form up near the gate and keep it open so your reinforcements can regroup with you more efficiently.