Checked what happens with the Pixie3 when "display on" is unticked, in other words the display is allowed to turn itself off.
Both GT31 and Pixie3 in the rear bike carrier, facing the sky.
Did two identical runs along the foreshore, one with display on unticked, then with it ticked.
The difference isn't the same as the xperia, here the pixie seems a bit laxy getting it's position, rather than having holes in the data.
Blue track GT31 Red Pixie3
All the running around on top of the houses are in the first 2 minutes while the phone finds itself. But even when it seems to have settled, it's out several metres in a north south direction.
After I come back home, turn display on, and go for the 2nd run, the tracks follow the GT31 much better.
In that first few minutes there are 3 false highs of 29, 26 and 23knots, but after that the speeds aren't too bad, but they're much better once display is on.
here's the GPSarPro view of the GT31 and Pixie3 speed graphs.
Yellow is Pixie3 Red is GT31. There's a marked difference once the display is on in the 2nd half.
I attribute the big spike in the middle to my body blocking satellites while I turned the display on.
Like the Xperia the Pixie needs a good view of the sky.