If I have understood correctly, the region which is set determines the shadow that is thrown in an undifferentiated way. However, I think region 1 needs to be different for the following reason. Take, for example, a small cupboard, table or sideboard next to a window. It's going to be region 1 as that is its height. Clearly it needs to throw a shadow - but the top surface of the object needs to be lit as the light will be falling on to it from a greater height if the window is a normal one. Perhaps there is already a cunning way of achieving this which I haven't noticed. If so, great. If not, is there any way to have this effect?