Did You get a chance to read that link I posted? Also, Myself and a few posters here use the SmokeDaddy Wood Burning Heat Diffuser in our Pellet Grills from RecTec Grills to Pit Boss... Meaning some have PID Controllers and some do not. The burning wood created a major temperature issue with temps running sometimes close to 200* degrees and higher over the set point. ....
If I can chime in here with a different observation...
I replaced the controller in my new PB700 with a Pellet Pro (it too has the fire box in the middle), and I noticed that the center of the grille actually ran cooler than the end(s) where the sensor is. The new controller has total control over the fan and pulses the auger to maintain a steady temperature. This resulted in a ~30* temp difference. I will need to do a couple more smokes to determine whether the probe should be moved closer to the center of the grill. Either that, or slide the sear cover over a bit to allow more heat in.
Mark