The only models I've flown that show any hint of ground effect are low wingers. And I'm not sure the high wing loaded ones showed anything at all. My Tiger60 shows it. Sometimes. I think. Maybe.

It seems to happen at about halfspan or about 3XC (3 chords) above the ground. But the model doesn't pick up speed (from the theoretical loss of drag) and since that's the most emphasized symptom in the flight text books, I'm guessing it doesn't actually happen. What does, is that sometimes the plane seems to not settle. And that could be other things. I've never noticed the text books say the plane will float and not settle. Just from landing performance, I'd vote that we don't experience ground effect with our models. And I don't know what or if the text books say anything about ground effect on landing. Anybody got a quote from a text that mentions landing?

BTW, the text quoted mentions 25% and 1/10 span for the meaningful effects it chose to describe. I would guess they did that because their perceived symptoms don't show up significantly and usefully outside that range. 1/10 span is probably about the height most landing gears keep the wing away from the ground. And above 25% span, a smaller reduction that 25% in induced drag doesn't do much for you or to your airplane.

We don't have instruments. Nor can any of us accurately tell the difference in airspeed that will happen with such small reductions in induced drag. And our model's extremely light wing loadings (in comparison to full scale) predispose our models to have almost no induced drag to worry about compared to full scale. So I'm voting with the guys who say our models don't show ground effect. I think they might, but I'm convinced none of us could see what the texts say happens.