How do you stop shadows from casting through meshes?

I created a simple demo scene to illustrate.

I have 2 cubes stacked on top of each other. Then I have a sphere that I place above of the top cube. I only allow the sphere to cast a shadow. Why does the shadow cast on top of the upper cube and go through it and cast on the lower cube as well? This is not ideal and I've been struggling for days trying to fix this. Adjusting the shadow distance in quality settings is not a realistic solution either as the distance should be unrelated to this issue. Shadows should not cast through meshes and I'm not sure how to prevent this from happening. Help would be greatly appreciated. Thank you!