The closer the object is to the background or other objects behind it, the narrower the shadow. In the illustration on the left notice that the shadow of the middle object is narrower where it hits other objects because they are closer to the top object than the background but wider where it strikes the (more distant) background.
You can take this realism a step further by varying the darkness of the shadow. The farther away from the background, the more light slips in between the object and background. So those shadows will be lighter. Narrow, dark shadows suggest objects that are close to the background. Wider, lighter shadows indicate that the object is closer to the viewer.


