The applicability of linear parameter functions for fitting the full-energy peak efficiency of Ge gamma-ray detectors has been examined in a wide energy range of 50-8500 keV, typical for prompt gamma activation analysis, by using efficiency data measured with the Budapest capture gamma-ray spectrometer. In a least-squares fitting procedure involving correlation and singular value decomposition the performance of six different analytical functions has been compared. It turns out that a high-order polynomial function on a log-log scale gives the best performance if a proper fitting procedure is used, as in the program Hypermet-PC.