I've received my "Proper" (jolly expensive) screen material today! I have to mount the frame about an inch off the wall as the wall is "natural brick" and rough. To avoid having my 2 year old poke her finger straight through it (as there will be an inch void between the material and the wall) I was considering nailing a piece of hardboard right across the back with some batons. Am I in anyway going to spoil the image? Not sure if the projector needs to project slightly through the screen like in a cinema and worried dark hardboard may interfere somehow. TIA, DAKS.