My GUESS ... If I understand you correctly ... Is that even though the tip of your probe was at about the same location height wise ... That the vertical probe is either not recording actually at the tip, or ... The hotter air is heating the probe further up towards the top, and the metal of the...
First off let me say I do not have one of these incubators, and am hoping that somebody posting here that is actually using one will chime in ... Hint-Hint ;)
When you say that your other thermometer says ... Have you confirmed it is accurate?
The problem with having two (or three)...