Expansion tank in CBO, why is that?

Question

Cooling systems

But it’s interesting, who paid attention to the thread that not a single CBO assembly was done correctly? Even all sorts of HyperPC and others collect nonsense.

The funny thing is that even the components do not exist in order to assemble it correctly.

Why is it wrong? The expansion tank in all systems is at the bottom or in the middle, and should be at the highest point. And over time, it is completely filled with liquid, while in the radiator, which stands at the highest point, it is partially filled with air (mechanics of communicating vessels). Yes, it is clear that part of the liquid is still pumped through the radiator, since it simply has nowhere to go in a closed circuit, but there is still an air lock there.

Why is that?