Jep, right. The extra code is just to give the system a little 'physical room' to prevent imprecision issues. So I move the face out, scale it down so it does not touch something, create the test volume, test, and then go back to the original shape with the result, deleting the rest of the geometries that were created for the test. I know it's a little complex, but that gives the best results.
Nevertheless, in your example, I'd try to not use Occlusions, but really try to well-define all your shapes, so you can guarantee that e.g. signs only get placed where no building is. Maybe post a screenshot of the desired situation and I have an other input.
Lemme know !
Interesting topics you post ! 🙂