So far with this installed I've only played a single town siege, so my findings are limited to that experience. There will be more later though.
I noticed the AI guarded all of the entrances, and not just one. This is good, and bad. It prevents me form attacking a completely unguarded side, but if I focus everything on one side (which I normally do) their defenders are of course spread thin and 3/4ths of them are idle.
I started shooting out a section of wall with a catapult, the Archers moved off of the wall before it "popped" them off. But, they moved off that entire section of wall when it was less than 50% destroyed. I did this little bit of damage to three spots and the whole front of the town's walls were vacant. Their Archers retreated off of the walls and therefor were useless in the actual defense.
I blew open a section of wall and then blew off the towers nearby to that section. The AI didn't really gather by the opening, so my guys were able to spread out on the other side of the wall. They didn't get surrounded as they usually do in this situation. I put my spearmen on Guard and lined them up at the three streets to block whatever units came to help while my ostmen killed off the units within the perimeter. Those that tried to rout of course ran int my spearmen formations and got eaten.
The archers that retreated earlier returned, but they actual l charged into my spearmen in melee. They didn't use their bows at all, so they definitely shouldn't have been out of ammo. My spearmen, with my archers behind them routed them after their numbers got low and I moved up all of my lines, replaced "tired" or worse units with "fresh" ones. Moving the "tired" units outside of the walls to rest.
The enemy came out of the plaza to attack my spearmen until they routed back to the plaza, and each time I moved my guys up a little bit and kept the General right behinde everything to keep my guys morale up, and of course I replaced "tired" units with "fresh" or "warmed up" ones as needed with 2 archer units behinde the lines helping the enemy rout faster, and slaughting the enemy when they did turn their backs to rout back to the plaza.
This continued until I was at the plaza itself, with my guys "warmed up" and "eager" the enemy units couldn't step outside of the plaza without going "steady" "shaken" "wavering" "routing" quickly. Their general came out, but didn't do too well against my spearmen and archers. They were literally trapped within the plaza at that point, surrounded and couldn't leave to even try and fight without routing. My archers took out the rest of their archers first and then I simply rotated my archer units until their army was dead.
I am focusing on siege battles because 1. They are the most decisive battles, 2. They are, to me, the ones in need of the most attention. Let's check out siege #2. This is a bigger town, with stone walls!
Here is my army's make-up. Catapults up front (out of the missiles' range) with everything else lines up behind. The enemy didn't spread their units out at all of the entrances this time, just two.
I pick a section of wall, and start shooting at it with both catapults. At 38% health on the wall, the archers run off the wall. I'm going to need an entrance so I finish blowing up the wall. Gates, I don't go for with catapults because their trajectory makes actually hitting the gate itself difficult, that and you need to take out the gatehouse as well.
I repeat on the other side of the gatehouse, at 38% the archers and spearmen (why would spearmen even be up there. I don't have ladders.) retreat form the wall. For whatever reason when they retreat from the second half of the wall, their towers suddenly are able to reach my catapults and start shooting at them like crazy, I lose a few guys but back them up ASAP.
Now their walls are vacant. This makes my approach much easier, since they have no missile units on the walls at all.
and the siege continues...
You don't even need to be "on" the walls to activate the towers. You just need a unit nearby, archers work fine too.
Another thing I've noticed is my units in melee spread out quite a bit. The melee units will have 2 guys fighting each other while the rest of the units is backing away, this goes for mine and the AI's units. Happens the same way when in "defense mode" too.