Fortress defense?

Does anyone have some tips on defending forts? I can't seem to make my men do what I want them to do. If I order a unit to a part of the wall they often won't go where I want them to go, and when they get there they may or may not fire the cannons and they may or may not fire at approaching attackers. Even if they do fire at the attackers they'll often fire just one shot then quit. When the attackers repel up the wall they won't fight back unless you toggle them to melee. If you toggle them to melee some of them may decide to repel down the attacker's ropes where, unless the enemy force has already been decimated they'll be at a disadvantage.

Are certain types of troops better at fort defense than others? Are the smaller 60 man units better than regular 120 man infantry units?

Use cannons to shoot a hole in your own wall and defend it when the AI charges it. Dealing with the walls at current just isn't worth it.

The smallest wooden forts are the easiest to defend or the largest star fort for different reasons.

1. star fort has more buildings to garrison. If you have a large (full stack) garrison, Deploy all your good troops in a square around the center facing outward in every direction. Larger field of fire that way. If you have junk units let them man the walls over top the gates only. They will slow the enemy down and act as a meat shield.
Place any arty in the center. I like mortors only for this as the earlier cannons tend to want to shoot your own troops.
2. Small forts deploy your troops to cover the ramps, not on the ramps. put the crap units on the walls to act as a meat shield. Placing units in square shape (not formation , but for multiple units) to cover every fire angle. Let your general or cav hold the center. If playing in America or somewhere that have skimishers that can hide outside, place them outside the fort to shoot at units as they approach the wall...preferably from behind. Garrison the blockhouse only if you have a unit that will fit inside. Indian musketeers will not work as they "hide" instead of garrisoning the building.

If you have square formation researched having the unit closest to the gate should be in that formation to head off cav charges if they take the wall. They will also fire in all directions so they help with the side walls.

As already stated, if you can blow a hole in the wall quickly, the enemy will use the breach instead of anything else. So if they do blow a hole in the wall, that is where they will come thru. Place your units accordingly.