On Tuesday, July 23, 2019 at 8:31:54 PM UTC-5, wrote:
I have been using, selling, installing and servicing oxygen systems for hang glider pilots and soaring pilots since 1991. My age is getting to be a factor, my field elevation is at 6,200 MSL (Moriarty, NM) with altitudes of 17,999 MSL on tap. I now set the MH EDS system to 5,000 and start huffing supplemental 02 about five minutes prior to launch. I have learned that it helps with my concentration on tow, especially during the turbulent and demanding midsummer conditions in the high desert. The amount of O2 used from 6,200 to release at around 8,000 and a climb to 10,000 is negligible.

I'm with Mark Mocho on this. As a midwest flat-lander I start O2 out west as soon as I am in the glider (one less thing to forget after tow). My aged red blood chemistry is just not up to handling the thin air at the 5,000+ft airports that I fly out of. My MH EDS is always set to D5 and sometimes late in a flight I change to R/M for 5-10 minutes as a pick me up.