Sorry I can't help with that particular radio but I can answer some general questions.
For an optical kill switch to work the channel should change from full one way to full the other. Some radios thats 100 to -100, others its 100 to 100, whatever, look at the monitor, make sure its going all the way or nearly all the way from one extreme to the other.
Expo can soften the center of the stick throw, it can also make it more sensitive depending on which direction you go, best way to tell if you're going the right direction is use an abnormally high value, say 80 percent, and make sure it barely moves in the center and goes to full throw at full stick.