I've had this situation in my game today, watch out, wall of text.
I was trying to defend East Osgilliath (not repaired) today with Boromir and an army consistent out of 1 extra citadel guard, 2 spearman, 6 swordmilitia, 1 catapult, 1 swordman, 2 rangers, 1 Gondor archers and 1 gondor horsemilitia, most units had decent experience. Against a full stack of led by 2 nazgul generals (both with 10+ HP each!!), another General and at least 12 units of Uruks, luckly no trolls. So I was "only" outnumbered 2:1, and that should be easy when defending sieges.
It wasn't so easy.
I had 1 unit in my square, and had all my units behind the main gate. I usually set a few units at the left side right behind the gate, and a few units about 10 meters behind the gate, and no melee units to the right, but all my archers on the right, so my archer can should them straight in the side, without friendly fire, and more hits because they don't have to shoot with a big arc.
I had my citadel guard (not boromir) in shield wall formation and defense mode as first line of defense, together with the 2 units of spears, hoping they would hold them enough to get massive casualties with catapults and arrows in their flanks. But they rushed everything and 10 units of uruks just "pushed" all my +-700 men I had their to the side, so I couldn't hold them in place like you can in a field battle.
A small detachment of their generals and orc spearmen went to the side gate, so I brough 3 units of militia and my horses to fight them because all my professional troops were trying to hold the uruk horde in place. My militia and horses did an excellent job, killed 2 out of 3 generals and had 150+ kills each. However, my main forces who were put in defensive mode and spear mode got slaughter and my citadel guards (supposed to be elite forces) lost all 150 men, but killed only 20 uruks, my militia did WAY better. Same with every other unit who were defending the main gate, including boromir's unit had negative k/d ratio. I would have lost the game if it wasn't for my 3 archer unit who had 450 kills each (shooting from flank at huge masses = epic. And my catapult who killed 49 units
, in just 1 blow.
So now my final questions. What just happened? Why are my elites terrible and 800 men of gondor getting slaughtered right after the gate. Is it because of of defensive mode or shield mode from the guards. Because my militia who I ordered to attack did excellent, my elite horde I ordered to defend got rushed and slaughtered. Is it simply because of the sheer massive force (Mordor crammed about 1700 men, in just the side of about 2 normal units, they were that crammed, even moshpits in Metal concerts are not that crazy
. And how do I stop this for the next time?
To be honest, I would have had a better victory if it was just a field battle.