Quote "I rest my case. Quote

Not so fast______
"The effect begins to be noticeable when the aircraft's altitude is within 1-1.5 times the length of its own wingspan and, when the altitude is within about half a wingspan of the ground, the effect can increase lift by as much as 40%."

Yet another source, ______ yours is NOT conclusive____merely familiar to you.
There are MANY others and they do not all agree with one another.