I am using the Line 6 EX 1 Expression Pedal as a volume pedal on my Helix effects. Even after looking at all the settings I still have the same issue. When the pedal is in the heel position I get what seems like full volume but as soon as I start to move it down the volume goes to zero quickly and then back up as I go to the full toe position. It seems like the zero volume is at about 15% on the pedal and the volume sweeps either way from there. Any ideas how to address this?