Incubator Probe placement

I've got a 3 cubic foot wine cooler set up with 3 feet of 11"flexwat and a herpstat, using a 33cfm fan installed to the top blowing down, along the back side of cooler. When I use another probe ( Exo Terra and Coralife) i'm getting different temps of plus or minus 2-3 degrees. Different temps from top to bottom.

1. Where should I place the herpstat probe?

2. What type of temp probe to rely on?

seems a bit much with 3 feet of flexwatt I have a 5 half foot coke cooler that only has 3 feet of flexwatt. and as far as placement I let mine dangle right in the middle of the bator