It appears to actually follow the scaling of the screen ED is on. I moved it to my top monitor (1600 x 1200), and it was much easier to read. It went back to the unreadable size as soon as I launched ED. Opening with shift-mousover did make it expand down onto the ED screen, so maybe that's why it re-scaled. There doesn't seem to be a way to expand upwards, so I'm stuck with leaning way forward to read the compass.