Notice that Taras is sitting above his ground skimming machine thus greatly lowering the required height to still be in ground effect, unlike the cardboard device shown previously.
One thing I have done with a large R/C glider was fly down a very shallow slope that closely matched the glide angle in ground effect.
It's also good to watch sea birds using ground effect to skirt the waves as they roll in toward the beach. In this case they also use the air being displaced (for lift) by the wave as it moves. But even without a wave it is very obvious when the birds enter ground effect as their glide angle flattens out tremendously.
The landing area at the old SoCal HG site called the "domes" sloped down very gently and when the glider entered ground effect it became difficult to get it on the ground. I had many scary landings there where I came close to overflying the landing area because of that.
That's the LZ where Chuck Kocis was killed when landing. I considered it the worst LZ of any place that I flew frequently. Fortunately, I never had an accident there, but I quit flying there after Chuck's death. He was a good friend and I didn't like the site's vibes after that.
Frank C.