Browsing other threads, I found Can SLB drive a stronger Nema 23 Stepper Motor? - #11 by aarseneault which mentioned that changing the microsteps and corresponding travel resolution fixed their issue with dropping Z height.
After setting $152 to 16 and $102 to 400, I’ve run the same air-carve twice with no perceptible drop in Z height.
Hopefully this helps someone in the future.