rokija
The way to explain it is to use a plot of rate of descent (y axis) vs airspeed (x axis). You can simply get a few points each time you fly by doing an auto at a speed and note the rate of descent. If you get about 4 points from min RoD speed to max auto speed, the shape should be about right to find the best glide speed in any wind.
Just plot the 0 knots point about 30 knots to the right of the Y axis, to make room for the tail wind.
Here are some examples:
