I know there are many posts on this topic but I can't seem to get the answer(s) I need.

I have a mini fridge converted into an incubator. I have an 11" (wide) piece of flexwatt and use a Herpstat thermostat. I also use a Zilla temp gauge as another reading of the inside of the incubator and another Zilla gauge with the probe inside the egg box.

I keep the T-stat and the Zilla (for the incubator) probes on top of the egg box and pretty close to each other. The probe in the egg box is laying on top of the eggs.
The challenge I have is that they are all showing different temps. I trust the Herpstat the best out of the three but the egg box one has a temp of almost 2 degrees higher. I realize that the eggs will put out heat closer to hatching but they are only on their 3rd week since being laid.

I have read many posts and realize that some place the T-sat probe in the egg box and others outside the egg box. But . . . do any of you measure/compare temps inside and outside of the egg box, and what is more important? Should I keep the incubator at 88.5 F or inside the egg box at 88.5 F? Right now the T-stat is at 87 F and the egg box is already 89+ F!

I have already hatched out a clutch of 9 healthy eggs so I guess maybe I should not worry so much but for piece of mind I would like to know. (I was constantly trying to adjust the T-stat to keep the egg box within a small window of 88.5 F.)

Anyway, hope this makes sense and thanks for any answers.

Jim