It is believed that intrinsic efficiency is the material property and is independent of source-detector geometry. In the current study, we observed that the intrinsic efficiency varies with source-detector distance when point source is placed near to the detector. We present the variation of intrinsic efficiency of High Purity Germanium (HPGe) detector with source-detector distance as well as with photon energy. The variation in detection efficiency is mainly due to the variation of mean path length of radiation inside the detector. Monte-Carlo technique is utilized to study the variation in the mean path length of photon. It is observed that the mean path length first decreases, reaches minimum value and then increases with the increase in source-detector distance.