relation between rear side view factor and BkVFLss

[ynesse]

Hello pvsyst community !! 

can any one help me to understand the relation between these 3 values related on view_factor  

and this one in loss diagram   and this one in general simulation parameter in bifacial module    

I have learn also about view factor model in 35th European Photovoltaic Solar Energy Conference – Brussels, Belgium, 24-28 September 2018 article but I can't really understand how it calculate the view factor . 

thanks for advance