I would like to see ranged and siege units not be able to attack behind a wall. If someone is on the other side of a wall they can't really shoot through the wall. Of course after you get so far behind a wall the arc of the arrows/projectiles will allow the projectiles to hit their target. Perhaps if a unit is directly next to a wall they cannot attack the other side of the wall or be attacked. I don't know if this is easily done but its food for thought.

This has been discussed, along with not shooting over mountains or forests. The problem is that it involves line of sight (LOS) calculations which Req deemed far too number-crunchy to use in a game with the constraints this one has on it.

If this were done, consider that troops in a castle would have to be exempt, wouldn't they? Or only ones in towers, perhaps? It gets pretty complicated to see all of the ramifications of such a change.