How is the helicopter actually going to hover when it is in the middle of recirculation - as fast as it displaces air downwards (accelerating it) the air is deflected round the box and enters the disc from above with a higher velocity - therefore more pitch is required to accelerate the air which then goes round the box faster and enters the disc faster than the last time it went through - eventually the blades are having to work at such high AoA that they stall - so how is it going to get off the bottom of the box. There is no constant supply of slow moving or static air for the rotor to accelerate and therefore it will not lift the helicopter.