Lapp
You are the only one here claiming that no forced pressure is needed at high altitude when wearing a mask. Other people provided much more complete and authoritative postings than your, and to these nobody objected.
But he is still wrong. Take a look at this Embraer 145 manual, using the standard Eros oxy system.
.. Only normal (N) oxy selection is required for all flight conditions, and it is normally diluted.
.. Above 33,000' the mask auto switches to 100% oxy.
.. (The valves sense the pressure. Note that it says if there is a depressurisation the mask will auto revert to 100%.)
.. There is a backup manual 100% switch, if you require.
.. But constant flow (emergency selection) is only required to prevent the pilot breathing fumes.
.. (That is why it is called 'emergency selection', and not the 'above 35,000' selection'.)
This is what our system says too, if I can find the book...
http://www.smartcockpit.com/docs/OXYGEN_E1.pdf
Again, if you have a reference that says something different, then please provide it.