A practical air quality instrument needs a separator that will provide a consistent aerodynamic fraction of particles to the sensor element, rather than an unconstrained combination of coarse and fine particles. This paper presents an inquiry into the nature of a dual-stage silicon microfluidic virtual impactor as a practically manufacturable PM10/PM2.5 cascade based on geometrical parameters, manufacturing tolerance, simulated collection efficiency, and particle monodispersity measurements. In this particular case, the separator comprises a coarse stage with W1/D1/S1/M1/ϕ1 = 450/200/640/700/75 and a fine stage with W2/D2/S2/M2/ϕ2 = 250/200/280/300/75, with linear dimensions specified in micrometers and angular measurements in degrees. The simulation takes into account air density 1.29 kg m−3, dynamic viscosity 1.81 × 10−5 Pa s, maximum allowable deviation in silicon-on-insulator manufacturing process 10 μm, nine monodisperse aerosols from 1.5 μm to 15 μm, and actual testing with a TSI 6301 counter running at 2.83 L min−1. Simulated cutoff diameters are found to be 2.55 μm for fine and 9.90 μm for coarse stages, using linear interpolation and logistic function reconstruction. While having more gradual transition, the fine stage has a sharper cutpoint at a local gradient of 0.253 μm−1, with the measured points pushing the transition point toward 3.56 μm–3.79 μm. Coarse stage remains efficient above 50% threshold across all available monodispersive particle sizes, thus failing to completely determine its measured transition point. The primary observation is that cascade efficiency is determined not by the presence of the two cut points but rather by the fine-stage tolerance and stability of flow rate at the end of the cascade. Large channel width and feed flow rate have the largest influence on performance, small channel width influences mostly deposition, 75° branch angle determines the optimal compromise between trajectory separation and wall impact, and channel length primarily acts as a packaging parameter. The analysis provides a complete stage-resolved interpretation of a compact PM separator for portable air-monitoring modules.