<p>Accurate prediction of ionization in hypersonic reentry flows is essential for assessing plasma effects on electromagnetic wave propagation, including radio blackout and radar signature alteration. This work investigates the sensitivity of electron number density predictions for the RAM-C II flight experiment using the in-house CFD solver NExT. The simulations solve the compressible Navier–Stokes equations for an 11-species, chemically reacting air mixture in thermal and chemical non-equilibrium, employing a multi-temperature formulation for vibrational energy. A systematic sensitivity analysis is then conducted to assess the influence of chemical kinetic schemes, equilibrium constant formulations, vibration–chemistry coupling, wall catalysis, and three-dimensional angle-of-attack effects. The results indicate that the Park’85 mechanism systematically overpredicts electron density, whereas Park’93 and Kim show closer agreement with flight data. Incorporating fitted equilibrium constants and vibration–chemistry coupling significantly improves the predictions. Wall catalyticity also plays a major role, with a species-selective treatment—non-catalytic for neutral species and catalytic for charged species—yielding the best overall agreement with measurements. Three-dimensional simulations further reveal that small variations in angle of attack can strongly modify the local electron density through windward compression and leeward expansion; however, these effects weaken at higher altitudes, where diffusion becomes dominant. Overall, the study quantifies the impact of key thermochemical modeling assumptions on electron density predictions in hypersonic reentry flows and supports the capability of NExT to accurately capture weakly ionized plasma conditions.</p>