Dell mini pc Temps with and without fan

[tarantules]

I bought a used Dell Wyse 5070 thin Client with preinstalled Win11 Pro and I want to use it for ad-blocker with DietPi and Pihole.
I was curious about temps so I made some tests with HWinfo to see if is worth to add a fan for heat decipation.
I made 4 tests :
1st with no cooling fan and start from cold state (room temperature) for 10 minutes.
2nd with a 80mm fan on top of drilled case blowing air upward (pulling air out of case) for another 10 minutes.
3rd with no cooling fan but from hot state (was already warm from 2 previous tests) for another 10 minutes.
4th with same 80mm fan on top but now blowing air downward (blowing air inside of case) for another 10 minutes.
During the tests I had in full screen playing HD video at 1080p from youtube.
(The fan was connected via a USB adaptor with voltage regulator knob and was set at minimum rpm to keep it silent because will work 24/7).
The results was as expected except one pequliar thing I have not seen before and can't explain.
As you see from the screenshot below , the 4 Core's Distance to TjMAX was significant higher (case 3rd) with no fan at all than in case 4 with fan blowing downwards (in red rectangular) although the other temp values (in green rectangular) was as expeted to be.
How is this possible? What do I miss here? Can anyone explain this strange thing?

 

[townsbg]

It depends upon how the heat sink is designed. It might be designed to blow the hot air away from the cpu or designed to bring air towards the cpu. Generally you shouldn't change the fan direction on the heat sink. You also shouldn't be running your system at all without fans.

 

[tarantules]

This pc is fanless by design

 

[townsbg]

I'm not sure then unless it's better to blow the heat away from the processor. You'd be blowing heat towards the sensor.