All I can find are explanations on what causes delays with them on the battle map. I'm wondering how you get reinforcements on the campaign map. I thought it was if an army was on a tile touching the attacked city/army, they'd be brought in as a reinforcement, but when the Brutii attack Corinth with my faction leader right next to it, they're not brought in as reinforcements:
What do I have to do for my army to be brought in as reinforcements when the settlement siege starts?