The problem you have is the fact that all of the light sources you have mentioned here are creating a more global feel in the lighting therefore illuminating the areas you need to darken.

Without sounding patronising this really underlines the inexperience here with fundamental knowledge of lighting setups. Looking at the above image you can see straight off the bat by the ground shadow that its a globally lit issue as the shads are blue. You could use an occlusion pass but theres no point unless you understand what is happening with regards to the light sources you've mentioned, shaders do not matter here, they are irrellavent.

Try using a standard light setup first (key, fill and back light) then by using these you see how the lighting works.

Also its worth seeking out a book called Digital lighting and Rendering by Jeremy Birn - could save your life!

Jay