Well noted !
Yes indeed the results of the ground effect are almost non-existent.
But the needs are different.
Over water the surface is flat (I haven’t seen sloping water until now 
) and the ground effect only depends on the height chosen by the pilot.
In mountain riding the height of the ground below the plane varies constantly, and we fly over trees and other surfaces.
In this case the ground effect is more annoying than anything else.
I preferred to focus on the stability and precision.