To the OP - unless you can find an adjustable hydraulic-type switch to replace the Zero unit (I couldn't), I think you're out of luck with the OEM setup. I understand why Zero went this route - it's cheap, easy to install, requires no setup, etc. - but IMO a separate adjustable switch (like the vast majority of performance-oriented street bikes use for their brake lights) is clearly the way to go if you're serious about getting regen-braking activation exactly right for your riding style & brake-pedal positions, & independent of anything else.
This switch is inexpensive and has an extra-long spring to reach the brake pedal, but otherwise I have no idea how good (or bad) it is. To make it or something similar work, you'd need a frame bracket in the right spot with enough clearance to reach the brake pedal with the spring. If it were me I'd also install a mating connector on this switch to connect it to the OEM brake-switch connector for regen triggering, then rewire the OEM hydraulic switch to activate only the brake light (independent of the harness connection). Yeah, it's a significant amount of work - if I had a one-tool, 5-minute fix I'd share it, believe me.
Ray