Some shooting weapons such as stone throwers have an area template that the firer is allowed to place anywhere he wishes. This allows the player to deliberately aim his shot on a character model. Cannons also allow you to choose exactly where to aim shots, and so can be aimed directly against characters.
In the case of missile weapons that can be aimed in this way, there is a special rule which allows characters to either jump out of the way, throw themselves to the ground, or somehow avoid destruction by their amazing luck or uncanny reactions. This is intended to prevent characters becoming targets for these weapons in a manner which is unrealistic, unfair and definitely unheroic!
This rule applies to all missile weapons which work in a different way to ordinary shooting, and which are not therefore restricted by the rules regarding shooting at characters described above.