Mod control - continuous, smooth variation from min to max

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I'm trying to bring back some of my favorite sounds from the physical Chroma. One of them hasn't sounded right on the physical Chroma's even after repairing and re-capping the voice cards. I wanted to try it out on Cherry Chroma. It doesn't have a name of course, I just know it as "42" from my working program bank in those days. It's a filter sweep that is controlled by the Mod lever. I play it by holding sustain down, pulling the Mod lever fully down, and playing E1, E2, B2, E3, F#3, B3, F#4, B4. Then slowly sweep up Mod across its full range and back. Here's a clip from a 1985 recording that used it.

I noticed when I used the mod wheel from my Kronos to control Cherry Chroma's Mod by MIDI, it only moved positive, so I couldn't start the sound with the filters closed.
Looking at the data in MidiOx, I found the Kronos sends Modulation (CC 1) for moving the control up, and Breath (CC 2) for moving the control down).
I found in the CA help "That said, it can output negative values either by moving the control with onscreen with the mouse/trackpad, or by assigning a different hardware MIDI controller (by right-clicking, selecting MIDI Learn, and moving the desired controller). "

So I used MIDI Learn to learn Mod Slider with CC2. To get it to work on the negative side, I had to set Min to 50% and Max to 0.
This is close, but there is a "dead zone" near the middle, where I'm moving the controller but the Chroma is not changing so I can't get a smooth sweep. The Mod lever on the physical Chroma is continuous (as far as I recall) This dead zone appears to be the nature of the Kronos as a controller (I see a pause in MidiOx data as I cross the middle), but I'm looking for a workaround. Is there a way to map another controller or knob to Mod so that the full range can be controlled by a single parameter, so the middle range can be smoothly controlled?