ORIGINAL: acdii
I believe positive expo softens the control, while negative tightens it. I may have it backwards too. I would have to dig out the manual, but I am sure it is explained in there too, so RTFM.
Some radios it's called "negative" and on others, it's called "positive".
Some have a little plot that shows what the Expo is doing when you set it. Regardless, it should look like the sketch below. This is somewhat of an exaggeration of the shape, but the general idea is there. If the "bend" goes in the opposite direction, and if you fly it that way, please be prepared for some pretty radical performance.
CGr.