We show that stimulated polariton scattering in a semiconductor microcavity is observable over a wide range of laser pump angles. The ratio of idler to signal beams is found to vary strongly with angle, consistent with the expected variation of the photon fraction of the idler states, and the increasing probability of scattering of idler polaritons to the exciton reservoir with increasing wave-vector. The observed variation of threshold with angle is in good agreement with a semi-classical treatment of the parametric scattering process.