I was contacted by a person doing research on ion wind. After a lot of communication, it turned out that I was using different corona wires for VA-curve measurement and for sound measurement. For VA, the wire was likely 0.08 mm Cu.  For frequency response, it was 0.19 mm nichrome. It's hard to be sure (so many years have passed), but I dug out some photos, and the wires are obviously different

I have also made a crude CAD model of the thing. Find it in project files.