Good to know. I was wondering if that was the issueI think it's not a fair test. The flue probe is calibrated to read the temperature at the end of the probe assuming the dial is at a much cooler (close to room temp) temperature. Putting the dial that close to the stove will cause it to read high.
When I had a probe thermo installed in single wall, it would read high because of radiant heat from the pipe hitting the bimetallic coil. It's very sensitive to the installation.