Howdy Machinbird....
from the linked essay:
"An additional bonus of ground effect that becomes more significant as speed increases is called ram pressure. As the distance between the wing and ground decreases, the incoming air is "rammed" in between the two surfaces and becomes more compressed. This effect increases the pressure on the lower surface of the wing to create additional lift."
Bolding mine.....
Such heresy must not go unpunished. I do like the description, however, since it implies a 'cushion'.
Unfortunately, the word conjures up a visual of a "Whoopee" cushion.
We are not to use the word compressed, nor viscous, so I am exonerated for earlier offenses?
I will eschew the word cushion only, since 'air' is so effective in describing, well, AIR.
I will call my personal visual of ground effect: "Transient Atmospheric Gasket".
Hope no one beats me to GoDaddy.... TAG
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Lightning Mate has offered a very good point, that ground effect works best on a wing of low aspect ratio. My takeaway is that it is because the extended chord line makes a more concentrated area of "capture"; there is less loss of compressive force, since the wing is not skinny, but traps more air, for a longer time.