Terrain elevations now include the earth bulge correction, so the
profile visually humps up in the middle relative to the straight
LOS beam — showing how the curved earth rises into the signal path.
Uses actual k-factor from HRRR refractivity when available, otherwise
standard 4/3. For a 300 km path at k=4/3, the midpoint bulge is
~2,650 m (8,700 ft).