I just installed a plastic shower pan and am going to be putting densshield on the walls for tile. The plastic pan has a lip on it. I believe I can just run the densshield to the lip and then caulk between the dens and shower pan and the tile will come down to the actual pan? Or do I have to run the densshield over the lip? If I have to do that I will have to shim out the walls probably 1/2" in some spots. Thanks for any help with this and here is a pic.