After playing through a siege using the tactical rules in Battles, I was struck by how decisive the effect of multiple breaches really was. During a few turns with a single breach, it was fairly easy to just sit on the far side and smack whatever stuck its nose through with Readied attacks from three sides. But after the second portion of the wall was cracked (I totally underestimated how quickly War Mastadons can take out a wall!), the defenders had to quickly resort to attempting a lucky strike against the enemy general.
I’ve noticed that the fast-resolution combat system in Campaigns doesn’t seem to value breaches in the same way. On page 80, the only effect I can find for creating a breach is that it allows an extra unit beyond the “one unit per point of capacity” limit. It doesn’t negate any of the usual defensive advantages, so far as I can tell.
For example, let’s suppose a small army of 5 companies of tough ogre infantry and goblin wolfrider cavalry, plus a couple catapults (but no other useful siege equipment!), besieges a huge stone tower defended by a force of 3 companies of human infantry and archers. The commander needs to decide whether to attack, or to wait until the walls have been breached by catapult reduction and siege-mining.
With a tactical battle, this fight is basically impossible until they’ve breached the walls. Otherwise, the infantry and cavalry will just mill helplessly around the base of the tower and provide target practice to the archers. With a single breach it becomes feasible, and with two breaches the odds have swung heavily in favor of the attackers.
But in the Campaigns system they’ll already get to include all their infantry and cavalry for free, just because a Huge Tower has a unit capacity of 5. This means that there’s almost no point in waiting for the creation of a breach, since they have no effect on the outcome of the battle.
For battles that involve a sufficiently large fortress being besieged by a small force of powerful creatures (the scenario I ran two weeks ago), breaches don’t seem to help at all in the Campaign battle resolution method. That seems exactly the opposite of what I’d expect, since a small army of elite troops ambitiously trying to storm a large keep defended with mediocre troops would benefit substantially from some way to get inside.
I think the best way to rationalize the current rules would be to rule that the portion of the troops that are allowed to participate solely on the basis of unit capacity would always need siege equipment in order to participate at all, but the portion that participates based on breach formation can bypass the need for siege equipment. At least, that’s the way the tactical battle seemed to work out for us.
In practical terms, that could amount to a rule that the BR of the non-breaching units would be capped by the BR from their siege equipment, in a mirror image of the way that the BR from the siege equipment is already capped by their BR in the rules.