Reply to X1 Mapping Help!

I am trying to map the 3rd effects control (bottom two knobs) on my x1 so that they act like the filter knobs on my vci-100; I'd like to turn the knob left or right, and have it turn on automatically when i move it. When i return the knob to zero, i'd like the filter to turn off.
I've already mapped the 3rd fx amount to shift, and i've got the filter knob mapped, but it won't turn off at zero. What am I missing?