some questions about "pair style gay-berne"

for this command ,i just have to set “epsilon i_a,b,c” for each type and can set them to zero when i!=j .But for "epsilon " and “sigma” , i still have to assign their value for each pair of atom style right?
For i=j , i specify “epsilon” and "sigma"value . Should i do the same thing when i!=j?
If i use the command “pair modify mix airthemic”, what will happen for type i!=j about the value “epsilon” and “sigma” i just set?
Which one have the top priority?

The mixing rule for Gay-Berne is explained here:
http://lammps.sandia.gov/doc/pair_gayberne.html

and in the papers cited therein.

Giacomo