Yes, you are not going to get an accurate stove top reading that way. It needs to be directly on the steel top. I'm not sure the probe thermometer will be accurate when used on single wall pipe. Pen and I found the new Condar reading a bit high already at the upper range. With the additional radiant heat from the single-wall pipe I'm wondering if it's really accurate? This is not exactly a scientific test but could be worth a check. When the flue temps are high, say above 800F, take your stove top thermometer and temporarily put it on the flue pipe about 18" above the stove and let us know what it reads. The flue gas should be roughly 1.5 times this surface reading on the flue pipe. If it is accurate, try hard to avoid those forays above 1000F in the flue pipe. It's wasting fuel and pushing system limits.