Recently we have shown that the program DETECT provides a realistic platform to model the performances of scintillation counters with geometries as involved as that of the EXACT HR PLUS, a state-of-the-art position and energy encoding BGO detector manufactured by Siemens{ CTI for positron emission tomography, (PET). In this paper we present the results of new simulations of this block's performances updated to include the non-proportionality of the scintillation response of BGO, and the statistical noise from photoelectron ampli cation in photomultiplier tubes. The updated model accounts for the crystal dependent energy resolutions observed with 511 keV photons in the detector with excellent accuracy. Measured and simulated resolutions are shown to agree within-1% to +4% with an average absolute di erence of 1% over the entire block. The impact of the non-proportional scintillation response of BGO on the energy resolution is shown to be relatively small compared to that of the ampli cation noise in the four PMTs reading out the block.