With my Asiair the ASI120MM is set to medium gain.
One thing to be aware of is you will probably need to use the little black nosepiece that came with the camera to fit on your guidescope.
On ZWO's little guidescope the mini is positioned just inside the scope with the black adapter all the way in.
You will find it a struggle to get a focussed picture otherwise.
In my setup with the ASIAIR, ZWO Guidescope and ASI120mini it works a treat...
Think I tried it on the laptop which is how I found out where to position it and it worked fine...
Good luck.
Chris