Liquid crystal on silicon (LCoS) displays have become the most attractive microdisplays for all sort of spatial light modulation applications. Among the different LCoS technologies, parallel aligned LCoS (PA-LCoS) are especially interesting. They offer unique capabilities as spatial light modulators (SLM), since they enable phase-only modulation without coupled amplitude modulation, and with millions of addressable pixels. In this work we evaluate and demonstrate the various capabilities offered by a novel and simplified physical model for parallel aligned liquid crystal devices (PA-LC), thus also applicable to PA-LCoS microdisplays. The model provides the voltage dependent retardance values, necessary for spatial light modulation applications, for a very wide range of incidence angles and any wavelength in the visible. First, it needs to be calibrated through a reverse-engineering approach. In this calibration, the values obtained for two of the three parameters provide the correct values for important internal properties of these devices related with the birefringence, cell gap and director profile. Therefore, the proposed model can be used as a means to inspect internal physical properties of the cell. Last but not least the model is useful to simulate the retardance for novel PA-LC devices as a function of the LC compound and cell gap. Therefore, it is not only a reverse-engineering model but it also constitutes an analytical alternative to the usual numerical approaches for PA-LC devices design and construction.