When hovering in ground effect, the helicopter experiences an INCREASE in performance, i.e., the helicopter can lift a heavier load at a given power setting than what is possible if hovering out of ground effect.

Basically the ground effect is made up of two components:

- The vortices coming off the rotor blade tips are reduced in strength thus reducing induced drag.

- Air passing through the rotor disk from above is accelerated downwards towards the ground below. Because the ground to some extent prevents the air from getting out of the way quickly, the air can't accelerate as rapidly as it does when the helicopter hovers at a higher altitude. This reduction in induced flow velocity doesn't reduce the angle of attack of the rotor blades as much as it does when hovering out of ground effect.

Some food for thought: Have a look at the graphs below. They display results of static thrust measurements as a function of power input. In the left graph pitch is kept constant, in the right graph the diameter is kept constant.
As you can see, for "normal" model aircraft propellers, static thrust is almost independent of pitch, but depends strongly on the diameter.

/Red B.