I can't see anything wrong in your settings. Try these tow option, images attached. This is what I meant with more samples.
I take it the 3D model is clean, like no gap to the wall ?
If this is not helping you are welcome to save an archive and attach the file here. Then I will have a look.
AC 3 to 26 -Windows 7 - 24GB - 8core 4.4Ghz