Now we're entering a surreal world: "While taxing downwing at 10kts in 10kts of tail wind you have lost the ground effect due to the ground moving below you although you are in hovering in still air."
Hovering (as per original enquiry) downwind is not the same as a downwind taxi. In the hover, you are flying backwards relative to the air. But your position over the ground doesn't change - that's what you're trying to achieve. The ground effect will still be present up to about 8 ft AGL.