That sounds very American to me...
SWTT,
Not really, just ICAO CNS/ATM principles being applied, as the traffic density increases or decreases, so does the level of CNS/ATM resources employed, to maintain the design separation assurance standard.
As to US, the whole ICAO airspace model is based on the FAA model, because the fundamental model, and the underlying design principles, were based on the many years of demonstrated safe outcomes of the US model, with traffic densities higher than anywhere else in the world.
So, having E above C is perfectly consistent with the risk management model, as has been proved for half a century or so in US.
If you want to have a looks at a "really interesting" model, have a look at India, and there is plenty of air traffic withing and through Indian airspace.
Tootle pip!!