Solar flares may be an issue (though I stopped reading the New Scientist many years ago, having decided a lot of the content is garbage) but there is no "setting" on a GPS. A GPS computes the 3D fix, or it doesn't.
The SIRF-3 chip used in all cheap receivers today is pretty well corrected for altitude - within maybe 20-30ft. The SIRF-2 had the famous 200ft error.