I have an Auto Meter WB in my car, too. Check your Auto Meter documentation, you can program the output voltage to reflect any AFR you want, it's called "BGD Range Setting Mode" within the gauge menu. Here's the info from Auto Meter, it's on the bottom of page 4:
http://www.autometer.com/download_instruction/1143A.pdf
You can scale the output, meaning you can have the gauge output 0v for 10:1 AFR and 4v for 16:1, 20:1... whatever.
So if the gauge isn't outputing the the 0-4v range to the scale that the calc_pid is expecting, it's going to be way off.
What is your calc_pids.txt expression that you're using?