The performance of the Vertical Sectorization (VS) system has been evaluated previously using an empirical propagation model and a regular network layout. In this paper, our aim is to investigate the gain of the VS system under a more realistic scenario. A semi-deterministic path loss model run on a detailed 3D digital map is used for the evaluation. In addition, a real-world network layout and user density map is loaded into the simulator to represent a typical medium-size European urban city. The study shows that the empirical path loss model tends to overestimate the gain of the VS system, due to the fact that it is unable to take the complex relationship between the path loss and the antenna pattern into account. Both the size of the inner sector dominance area and the user density in the inner sector are critical parameters for the VS deployment, as low gain is observed for VS when there is no or very low number of users in the inner sector. As a result, for accurate network planning, a reliable 3D propagation model is required.