To simplify the activity, the following is my impression of what will take place during a vertical (no forward velocity) autorotation to the ground.
There is no change in the collective or cyclic stick, therefor the pitch on all blades, at all azimuths, and at all heights above ground, will not change. Near the ground the rotor disk's mean angle of attack will increase because of the pressure (attempted upwash) below the blades. This will increase the area of and the thrust from the driven (outer) region of the disk.
This increased angle of attack will reduce the descent rate, partially because of an additional pressure created under the fuselage, and partially because of an increase in the induced thrust. The induced drag will also increase. This is because the higher pressure (attempted upwash) will be attempting to pushing more air from under the blade upward, and some of it will move forward and up around the front of the blades.
The rotor's rpm may not slow because the additional thrust will increase the coning angle and the Coriolis effect.
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The above only relates to the rotation energy in the disk. Should the helicopter also have forward velocity, then it will also have linear energy. This will result in additional effects, similar to those experienced by a plane's wings or a gyrocopter's rotor disk. These additional effects must then be combined with those from above.
Just a reasoned guess.
Dave J.