How to change the radiance modifier properties of the soil?

Hi all,
I am testing the impact of the street width on the average illuminance in my building. It seems that when I make the street width narrow (i.e. 2m), I see an irregularity that the ground floor achieves more illuminance than the first floor. This makes me think that the soil impacts the reflection of light. So, how can I change the modifier properties of the soil?
I am doing annual daylight simulations (HB annual daylight).
Thanks,
Berrak