Attatched are the overlayed compton edges for the calibrated experimental and the GEANT4 simulations. Note p1 and p2 denotes the lower and higher energy compton edges for Yttrium.
The experimental and simulated histograms are shifted in quite a few of these plots suggesting the calibration was not fully successful. The compton edge for AmBe was difficult to locate and may have contributed to the poor calibration.