This paper is focused on discrete scintillation imaging devices, made by using crystal arrays and metal-channel dynode Hamamatsu 1" and 2" square Position Sensitive PhotoMultiplier Tubes (PSPMT). These devices are particularly suitable for nuclear medicine based high-resolution Single Photon Emission Computed Tomography (SPECT) applications. A more adequate analytical model describing the light-output spread from a single crystal-pixel, was studied. Previously experimental data published by us were reviewed using this model. The parameter which describes the intrinsic pixel light-output spread was obtained using an 1-D model-version, that adequately fits the measured single-event charge-strip integrals. Furthermore the intrinsic spread was found linearly dependent, in the examined experiments, on a crystal-pixel shape factor (defined as the ratio between the pixel-blind-surface-area to the pixel-volume). Finally, a simulation tool was developed on these basis, to predict and to optimize the imager response by evaluating the impact of each device component on the response.