Troops occupying elevated positions such as hills and the tops of buildings, can see over the heads of models, over the tops of lower hills, and over lower buildings, trees, and obstacles. This enables them to shoot over the heads of models below them.

Not only can such troops see and shoot, but they can also be seen and shot at because they are standing high up, exposing themselves to view.

One of the most useful aspects of this rule is apparent when you have a unit deployed on a hillside: models in a rear rank higher up the slope can see over the heads of ranks in front of them and so can shoot. This can enable many more models to shoot than is possible over level ground where only the front rank is able to bring its weapons to bear.