On Thursday, June 20, 2019 at 7:31:37 AM UTC-4, RR wrote:
Flying in wave conditions with 50kts of wind, I got "low" and the computer indacated a marginal glid home. I dug out until I had 3000 ft over glide (MC 2). Considering the was more than a slight chance of wave sink on the way home, I thought I should crank up my MC as one might do on a thermal flight to insure you are looking at info with some increased margin. Rather than lower my arrival, it increased it to 5000 ft. A fence post case to be sure, but the point for this thread is, you can try fiddling with your MC when flying in wind to see if you can see a difference in arrival height. I had never seen it "reverse" like this in thermal conditions (might happen between 0 and something low) but you can try.

I have always used the rule of thumb for glide into the wind, but in 50kts you can run out of fingers to count on...

It is convenient to assume that a higher MC setting is "more conservative", but clearly that is not always the case. Presumably the "MC" for the purpose of a final glide just meant that your computer assumed you will glide at the still-air MacCready airspeed for that MC setting. But the computer also took the wind into account when computing your achieved glide ratio and thus arrival altitude. Thus when you set a higher MC the computer read it as a higher airspeed, which was advantageous in this case of flying into a strong headwind. Thus it displayed a higher arrival altitude.

I think in this situation one should first decide on the speed to fly (would be nice if the computer would help you with that choice, but it may not). With a 50-knot headwind obviously you'd pick a rather high speed. Then adjust the MC until the displayed STF fits your choice of speed. Then see what it says for predicted arrival altitude, and add a safety margin to that in feet of arrival altitude, not in MC setting.