What determines how much structural damage a stack does?

Question

In order to quickly break down the defenses of an enemy town or fort, your creature stacks have the option to attack the door and the walls. Sometimes my creatures do 1 structural point of damage, while at other times they do 2. What determines how much structural damage a creature stack does?

Answer 1

The damage is determined by the physical size of the unit.

A unit that needs one tile does 1 point of damage. A 2x2 unit does 2 points damage.