Peuce. No. That is the ICAO semi circular rule that my team introduced.
Before the AMATS changes in 1991 we used the Quadrantal Rule and IFR and VFR flew at exactly the same level. That's why they were all in the system and had to operate full position reporting when above 5000'.
In fact FS gave traffic and didn't even mention if it was IFR or VFR. It was irrelevant .
Interesting how most can't even remember the system that they fought so hard to keep. It will be the same a couple of years after we finally introduce NAS.