Why? Sky wave fading results from signal polarity changing randomly due to unstable reflection. Drooping elements downward from horizontal to 45° will (in theory) entirely mitigate this aspect of the problem. The trade-offs are twofold: reduction in gain; elevation of take-off angle. Said solution need not be all-or-nothing. One might choose to meet it only part way. Plots below quantify these sacrifices. Shown are thumbnails, click for full size.
* Leading Half-Angle. Ref. Definition
Droop = 0.0° 8.58 dBi Azimuth Gain @ 0° Elevation
Droop = 5.0° 8.57 dBi Azimuth Gain @ 0° Elevation
Droop = 10.0° 8.54 dBi Azimuth Gain @ 1° Elevation
Droop = 15.0° 8.48 dBi Azimuth Gain @ 1° Elevation
Droop = 20.0° 8.39 dBi Azimuth Gain @ 1° Elevation
Droop = 25.0° 8.27 dBi Azimuth Gain @ 1° Elevation
Droop = 30.0° 8.12 dBi Azimuth Gain @ 2° Elevation
Droop = 35.0° 7.93 dBi Azimuth Gain @ 2° Elevation
Droop = 40.0° 7.69 dBi Azimuth Gain @ 2° Elevation
Droop = 45.0° 7.38 dBi Azimuth Gain @ 2° Elevation
Droop = 0.0° 11.34 dBi Azimuth Gain @ 26° Elevation
Droop = 5.0° 11.3 dBi Azimuth Gain @ 27° Elevation
Droop = 10.0° 11.26 dBi Azimuth Gain @ 27° Elevation
Droop = 15.0° 11.2 dBi Azimuth Gain @ 27° Elevation
Droop = 20.0° 11.13 dBi Azimuth Gain @ 28° Elevation
Droop = 25.0° 11.06 dBi Azimuth Gain @ 28° Elevation
Droop = 30.0° 10.96 dBi Azimuth Gain @ 28° Elevation
Droop = 35.0° 10.85 dBi Azimuth Gain @ 29° Elevation
Droop = 40.0° 10.71 dBi Azimuth Gain @ 29° Elevation
Droop = 45.0° 10.53 dBi Azimuth Gain @ 29° Elevation