Our fingers are a poor test instrument because they become uncomfortable from 45 °C upwards. Sure, cooler is always better, but you don't have to overdo it and as I said, fingertips are just too sensitive.

Even 60 °C is not a critical temperature for electronic components. CPUs in computers and on graphics cards can reach up to 90 °C. I don't like that either, but I'm only saying that to provide a comparison.

It will probably be a bit warmer inside the case, but the case is basically designed so that the heat is dissipated well to the outside; otherwise it would build up too much inside.

That's why, with passive cooling, you should leave a little air around the device. Not only on the sides, but also on the top and bottom, so that slight air movements in the room supports to dissipate the heat. By this, heat cant accumulate too much between devices, especially if they are placed on top of each other.

Therefore, in my 19" Rack I leave at minimum 1 finger broad room between devices (UFX III, 12Mic, Octamic XTC).
So I got a 4 RU rig but mounted only 3 devices (3 RU) to have that space.
Additionally, I took the shortest rack possible, 23 cm depth so that the airflow is also supported by this.

My proposal to you: first create your own facts by placing the devices individually with much room on top and on the sides without placing them onto each other, and measure the temperature again at the same point on the housing.

Now increase the distance to the table by placing something under the rubber feet to create more space on the underside for better airflow. Re-measure .. what is the difference?

Then compile the data and you can see what difference the two variants make to the current situation.

Make also a note about room temperature so that you can compare between summer and winter if the temperature is matter of change. Here it changes between 22 °C and 32 °C in a hot summer.

After having this data you can make a better decision
- whether the stacking of devices, separated only by the devices feet is well enough and
- as to what you prefer...

If the difference is not that much, then keep it as it is. Then I would take the temperature on top of the case as a good sign, that heat is being transported to the outside ...

With a cheap temperature measuring device I am getting around 36.4 °C at the center of the surface of an ADI-2 Pro FS R BE.
At other areas up to 37 °C. The device sits on top of a Thomann rack using its default feets and it is running since a few hours.
At that temperature you can keep the hand on the surface of the device easily without any pain.
Room temperature 24.8 °C.

Yes then your temperature really seems to be too hot.

Thats why I suggested to make comparisons.

When using balanced headphones the temperature may increase.