I'm not convinced that it doesn't matter how big the plate becomes. Take a setup (meaning a combination of rotor-to-plate separation and plate size) that won't hover. Imagine you quadruple both the separation and the plate "diameter". Now imagine that you look at the setup from four times as far away. From this perspective, it appears that the separation and plate diameter stayed the same, but the ROTOR diameter got 4 times smaller. Getting back to the original setup where the helicopter wouldn't hover... would you expect to be able to make it fly by reducing the rotor diameter? (remember that part of the thought experiment was that the weight of the plate didn't change as it got bigger). I think you always can make the plate big enough to prevent hovering (at least in "steady state").