So, I did some testing. I used the “Hardware Monitor” app to compare temperature readings between the vertical (portrait) and horizontal (landscape) screen orientations / rotation. Then I run 3 consecutive tests with CineBench R20. Each cycle takes 10 minutes on my computer so each orientation was tested for about 30 minutes at full CPU load. Then I took a screengrab of the sensor overview window of the “Hardware Monitor”. I did the same for both orientations. I ran the horizontal first, then the vertical outing the imac to sleep for a couple of minutes to change the orientation. Note that the ambient air temperature is higher on the vertical orientation. I also include a screen grab of the Intel Power Gadget as it was right as the 3rd test cycle was ending at the vertical orientation. I believe this app is showing a more accurate reading for CPU temp. Note that while the hardware monitor app is old and discontinued, it and my iMac are of the same era.