The installation of an advanced plasma position reflectometry system, aimed at complementing magnetic sensors for plasma position and shape control, is foreseen on the DEMOnstration power plant (DEMO). For such a system, we presented in 2018 the G3C boundary reconstruction algorithm, based on the plasma-wall distance reflectometric measurements and on the values of the plasma and poloidal field coils currents. This work presents the upgrades implemented to the algorithm and its application to both the DEMO baseline and several non-baseline scenarios. The algorithm is further applied to reconstruct the plasma boundary during a vertical displacement event. Results indicate that the method is able to estimate plasma shape parameters and position with a remarkable accuracy, provided that reliable reflectometric measurements—within 1 cm accuracy—are used as input. Furthermore, it shows significant robustness to higher measurement errors for what concerns the estimation of most of the plasma shape parameters estimation. Overall, G3C proves to be an accurate, reliable and flexible reflectometry-based boundary reconstruction tool.