An optimisation of the geometrical model of a p-type detector used for material screening was carried out to improve the accuracy of Monte Carlo simulations in reproducing spectrometric measurements. Gamma-ray sources were measured to determine the dimensions of the detector dead layer and borehole. An agreement between simulations and measurement within 3% was achieved at energies above 100 keV. In contrast, discrepancies on the order of 23% were encountered using the nominal parameters from the detector manufacturer.