A programmable LCOS reflective spatial light modulator using an array of liquid crystal pixels used as a phase modulating device is studied. Modelling has been performed to determine the pattern of electrode voltages required to achieve a blazed grating with a linear phase ramp and an abrupt phase transition. As two-dimensional steering of incoming wavefronts is required, oblique gratings are also considered and the effect of the angle of the pixel grid with respect to the phase front of the grating is also considered. Here we study this effect using two possible configurations of the director pre-twist.