Simulation is widely used for performance analysis of Personal Communication Systems due to their inherent complexity. However, resource demands (cpu-time and memory requirements) for this type of simulation are often high. Consequently, simulation fidelity demands must be carefully weighed against available computer resources in modeling. In models including measurements of interference from other transmitters, one question that arises is up to what distance other transmitters must be included. This parameter has a direct impact on the amount of work performed in each interference calculation, and is also of great importance for parallel and distributed models since it influences partitioning. In this paper, the impact of the interference (or interaction) radius on fidelity and execution time is studied for a case model.