HB Irradiance with BSDF unusual results


I am running a radiation analysis using HB Irradiance. I have used a BSDF file (using HB BSDF modifier) for a combined window and venetian blind (45° closed and 80° closed). However, looking at the results, it seems a little strange that the radiation seems much higher at the top of the window compared to the bottom. i have used LBNL WINDOW to generate the BSDF File. Could there be an error with the BSDF file that i am missing?