This confused me too at first and I think I even started a thread about it but once you know
 
1 left = mono input 1
1 right = mono input 2
 
2 left = mono input 3
 
2 right = mono input 4
 
etc... it is very easy to figure out. You got it now. There are far more confuzzling head scratchers that lie lurking and waiting for you. Don't worry about this one. ;-)

My hat's off to those of you who condone Sonar's pathetic attempt at describing inputs. I personally believe it's pathetic... Peace, out! :)