Phase-to-ground faults are the most common type of fault on overhead lines and require accurate detection and selective isolation by distance protection systems to ensure reliable energy transmission. Conventional distance protection relays analyse the impedance of the phase-ground loop of the affected phase, utilizing line impedances to configure protective settings specific to each line. Accurate setting parameters are among the most critical components in a distance protection relay, as they are essential for determining the correct fault location. Improper configuration of these settings can significantly reduce the efficiency of the entire protection system. These settings include the symmetrical components of positive-sequence and zero-sequence impedances, along with the resulting ground impedance compensation factor, so-called K _E-factor. Building on a previously developed line model that realistically simulates overhead lines -including finite length of ground wires and tower propagation resistances-this paper explores the sensitivity of the zero-sequence impedance and the ground impedance compensation factor in distance protection relays by analysing the impact of variations in influencing variables. A case study illustrates discrepancies between calculated and measured impedances in real overhead lines. Further, potential errors in impedance determination, such as inaccuracies from oversimplified mathematical models, are also addressed, highlighting the influencing variables that affect zero-sequence impedance and K _E-factor.