One of the main advantages of continuous scintillators is the excellent depth of interaction identification capability. We present the results of the Monte Carlo program OPTICS simulating the light response of a gamma-ray detector module comprising a continuous scintillator and an avalanche photodiode array to determine the effect of scintillator surface treatment on the ability to determine the three-dimensional position of interaction. We investigated the effect of optical coupling compounds, surface treatment, and depth of interaction on the distribution of scintillation photons reaching the photodetector pixels. We show that a black coating material without an air gap leads to improvement.