Abstract: This paper,the fourth in a series,describes the parametric corrections for summing effects caused by cascade-crossover transitions. The definition of "total response of Ge detector for a single energy γ-ray" has for the first time been clarified with scattering γ contributions at low energy regions included. Peak to total ratio (P/T) has been proven to be dependent of counting geometry and measurement surroundings. This P/T definition has been verified on nuclides with typical cascade-crossover γ transition (e. g. 75Se). Nuclear parameters related to summing effect corrections have been tabulated for 72 nuclides of NAA interest.