The CPE value is influenced by the formation of the compact layer and the mobility saturation effect arising from the finite size of ions. Figure presents the predicted CPE values as a function of the hydration shell radius of cations. The model predicts that larger hydration shell sizes lead to greater deviations from ideal capacitive behavior, as increased ion size enhances spatial heterogeneity in both conductivity and permittivity, reinforcing the CPE effect. This trend is consistent with experimental observations: as illustrated in Figure , the non-ideality for lead ions is more pronounced than for cadmium, which in turn exhibits greater non-ideality than zinc.