Thanks for your quick response! I had tried researching this issue before posting and it seemed like the ground through the PC was enough (it's not connected to a laptop). I tried a direct earth ground connection as you can see here. I apologize for the messiness.
But as you can see, the results are still effectively the same.
Any thoughts on what to try next?
Also, any thoughts on why proximity isn't being detected? I'm using a 7.6M ohm resistor, which seems like it should be picking up something other than direct touch. I'm guessing that the issues are somehow related.