you could also see about throwing on the walls close to you on a transparent layer so you can see through them, but still see that they are there... It would allow you to use the same tiles without having to change them at all.. if you were really creative you could make it a mask instead of it being entirely transparent, and create a more fluid visual effect (making the bottoms of the foreground walls almost fully visible and have them fade out more to the top... lots of work, but i think transparent would be acceptable...