How to calculate snow particles'reflectivity?

[Nobabessba]

I set m=refractive.ice_refractive('ice_refr.dat')(8.43,0.2) and mu=0(GammaDSD),the other settings are the same as the example given by Wiki which is to compute radar scattering properties for a C-band radar. The result is too small(ref=9.55dBz WhenD0=1.1,Nw=2500)