DublinPilot
That was not pointed at you
and maybe its me that is being totally stupid
Standard pressure is just that an artificial figure which if your lucky may coincide with an actual presssure of 1013 but is very likely to NOT!
It is the actual pressure which is relevant to Hypoxia.
There can be a huge variation from Standard high or low meaning the aircraft can be higher or lower than the standard pressure setting level showing on the altimeter.
Hence I find it hard to see how a flight level can be used with accuracy without reference to the actual pressure or at worst regional pressure setting
Pace