Airflow and temperatures don't have anything to do with each other.
Umm.... Time to go back to school if you think that is the case ( Pun intended ).
You do realize the reason we have fans is to push out Hotair from the computer right?
The Primary Purpose of these Fans is not to actually "Cool The Air"
Airflow has nothing to do with temperatures? If air can't escape and hot air stays inside the case because all fans are trapping hot air in what happens?
If The Intake isn't pulling cooling Air in and Hot air is trapped in the case what happens?
If The Exhausts are all blocked due to dust or poor placement of the PC what happens?
This is essentially "Air Stagnation" where hot air can't leave a room hence it keeps heating up. Cracking a Window that doesn't have direct sunlight helps more than a side panel being open.
Removing side panel lets all that Hotair Escape - but it simply adds more to the ambient temperature. Which in turn heats up the environment around it which will increase the heat of the PC in turn. Now that the side panel is off your fans are working less efficiently as well.
The problem here is a small room that can't absorb enough heat. So unless you have an AC in that room to keep the temperature cool the setup location is the issue. Big Rooms can absorb a lot more ambient heat keeping shades closed to prevent excess heat is more than enough for your PC to manage. Or Windows closed if your AC is on.
If you don't know anything about Airflow, how can you even claim your "Airflow is Perfect?"
You should probably have your PC confiscated at this point for making such an audacious statement. Pretty much the same as Animal Cruelty. I am officially revoking your PC license and prescribing you a console.