If you want your shadows to stop overlapping so that the whole shadow has the same color, you could do something like this: instead of having the ShadowCaster behaviour on your game objects, have it on some invisible placeholder that you place beneath your sprites. These placeholders must all be on the same layer. Set the ShadowLight opacity to 100%, and set the layer opacity where you put your placeholders to something like 50%. This way the shadows will be rendered together as a whole image with its own opacity.