Use of multiple fix gcmc commands

Dear lammps-users:

I have two questions about using multiple fix gcmc commands to simulate binary gas adsorption:

1.When we simulate gcmc process of mixture, how to set the pressure and fugacity coefficient?
Should we set the pressure as partial pressure? or just total pressure?
Fugacity coefficient of components corresponding to partial pressure or total pressure, which one should be used?

2.Can we set specific composition of each component when we use multiple gcmc commands?
For example, I want to set the mol ratio of methane and butane as 0.9/0.1 in gas reservoir. Is it possible to implement this with LAMMPS gcmc?

Any suggestion could help a lot. Thank you.