"Usually? Maybe. "Period"? No. A wing in ground effect is not creating enough downwash to account for the lift."
My thought on ground effect is that the wing functions in what is functionally denser air (ambient) due the piston effect of the wings. For a height of roughly one half the wing span, the air cannot escape the squeeze of the wing's downwash as quickly as in a fully 'open' region, the wing and ground proximity reduce the escape "area" between them; the local airmass is functionally, denser....