How to post-process the percentage of the species on a surface
 

Ciao!

I release a inert-mixture using species transport (without any reaction) from a surface in my domain with specified mass fraction of one (100%) and I want to know how much (%) of this released species will reach to another surface within the domain.
So with which feature in the fluent and/or CFD-post I can have this percentage?
I try facet average, mass weight average, but I cannot got the correct result by them.