Are you using the new driver or the old?
I had the same problem with adjustments at the lower end and conversation in the car. Here's what I found out:
I downloaded the new "improved" driver from the powermate site and it would only adjust in 2% increments at the lowest.
a re-install of the original drivers gave me back my 1% adjustments and all was fine in the world again.
Try driverheaven.com or some other such site to get the older driver as griffin doesn't seem to have it available anymore..............