Simulated daylighting illuminance problem in Honeybee

Dear All,

I am doing a daylighting simulation and compared with measured illuminance data. In my Honeybee+Radiance simulation results,I found that the positions with 4 meters away from the walls have the highest illuminance and the positions with 2 meters away from walls have very low illuminance values. But in the real measured conditions, I found the 2 meters away positions have the largest illuminance. I found this is very weird.
I set the ceiling reflectance as 0.8, wall as 0.6, floor as 0.3, column and ceiling as 0.6, outdoor ground as 0.2. Bounce -ab as 4, and all other kept as the default.

Does anyone know what could be the reasons?

Thanks a lot.

Regards,

David