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In a still air incubator, there are layers of air at different temps. The bottom, on the wire, is cooler than at the top of the eggs. You want the center of the egg at 100F. The top may be 102F, and the bottom 98F. That way, when eggs are turned, the temp gets distributed. You get an average of 100F. If you had 102F at the bottom, on the wire, your egg tops may be 106F.
So where (what level) you check the temp is very important. If you add a fan kit, that eliminates the different layers having different temps, so then you want 100F, period.
Since you are going by the temp at the bottom, on the wire, you may want to try for 98-99F. Good luck. Can you put something egg-height in the 'bater to set your thermometer (or probe) on, to see what your egg top temp is? That would be better than guesstimating it, if you can do that. You could cut a small section out of an egg carton, to set it on, if you have room. Some people place a thin piece of cardboard or plastic strip across the eggs, and set the therm on that for a while, to check temp.