Agreed. As long as you have good archers, you can mostly hold any massive besieges. Re-positioning your troops manually on better angles works best, but, like some cases you can't, the auto deployment could suffice.
It's random, most runs small factions falls, some runs they survive. But if it were me, I would take a town for Cretas, that should give them enough room to grow. Then, just stall defensively till they garrison their strength or until a ceasefire is called.
I love Ingvar custom mercs. I find them very fun and strong. I rely on them for everything, especially sieges.