I tried the shelf liner under the PCB already, and it made the feel slightly worse, more mushy. The shelf liner under the whole case made it feel better overall, but didn't help with the row differences.
I'm not sure how to explain it. If I hit the number row hard, there's a thock when it bottoms out, where it actually stops. The other rows feel more like I've hit soft dirt, and it's more of a thud. When just typing, the number row feels more "clean."