I plan to place a droppings board 12 inches under the roost in my small coop. The roost is 12 inches off the wall. Space is limited. Wondering how wide it should be so dropping land on it and not outside it? I will run it to the wall on the one side but not sure how far off i must be on the non wall side. Need to to use the minimum I can get away with yet still have it effective. Any suggestions?