Using Monte Carlo calculations, it is shown that the transmission of scattered neutrons or gamma rays from a point source through a plane slab of infinite extent to a point detector depends on the orientation of the slab but varies very little with the slab position. This is also true for reflected radiation if the source is replaced by its image source and the results are interpreted in terms of a transmission problem. It is also shown that the transition from a slab of small extent (narrow beam conditions) to a slab of infinite extent (broad beam conditions) can be characterized by a simple function of the single-scatter angle. This function, too, can be applied to reflected radiation by invoking the image source. Typical results are presented for polyethylene and iron.