Simulations of fluid flow across in-plane microvalves were performed using an advanced multi-physics commercial software system and compared with experimental data. Model validation required careful consideration of leakage pathways left by fabrication artifacts. Following model validation, the effects of leakage pathways caused by variations in sealant thickness were explored. These results were used to predict the effect of leakage gap thickness on the ratio of flow resistances across the open and closed valves. The effects of structural modifications on the valve performance were also explored in this study.