The traditional place to put a broody box, at least in some designs, was above the roost bars and off to one side. But you have to run it all the way to the rafters to keep the other birds from roosting on top of the box. Some elevated and hung it from the rafters to allow the other birds to continue roosting below if roost space was tight.
If you did put it below the roosts, you would need to use a droppings board, or at least a barrier of some type to keep the droppings from the roost above from hitting the birds.
BTW, it was also traditional in some designs to place the nest boxes on the back wall beneath the roosts. In that setup, droppings boards were mandatory. That was the case in Woods 6' x 10' back lot house.
I measured my Woods house roosts, and they are 13 inches off the back wall and 14 inches between each other.
If you did put it below the roosts, you would need to use a droppings board, or at least a barrier of some type to keep the droppings from the roost above from hitting the birds.
BTW, it was also traditional in some designs to place the nest boxes on the back wall beneath the roosts. In that setup, droppings boards were mandatory. That was the case in Woods 6' x 10' back lot house.
I measured my Woods house roosts, and they are 13 inches off the back wall and 14 inches between each other.