Siege Towers can load units then click on a stone wall, after the door opens, you can bring your units on to the wall. In order to add more, you need to load more into the tower.
The tower will behave like typical transport unit and immediately turn towards unit’s that are issued a load command onto one, then you have to reclick the wall and play the animation for the tower door to open again to go.
What should happen is the tower door is opened onto a wall, it should no longer be able to move and needs a separate dislatch command to regain control, any unit issued a load command onto a tower in its latched state should automatically be deposited at the top of the wall.
Walls should also be leavable if units are ontop. if a wall does not have a gate or tower, your units that you put on with a tower cannot go down the other side.
Also, why can a cramped ram fit 16 people but a more spacious tower can only fit 8.