Since Ive never done a true auto on purpose Iam not an expert on the subject. I have read alot about the dynamics. I do know that once you lose power whether in a full scale heli or model the same things apply. First off you cant give full positive pitch at the moment of power loss or you lose to much rotor speed.You must allow the rotor to maintain as much headspeed as possible, And in bigger craft you actually have to dive to preserve and increase rotor speed so you have it at the bottom where you need it. hence the higher altitude that was mentioned. if you are giving full pitch or throttle right at power loss your killing your main rotor speed to quick and you dont have enough rotor speed at the bottom to give you any lift to flare and land softer.
If you ever get the chance to see full scale helis do autorotations its really something to see, all heli pilots must learn this to get a license to fly. And it is the only chance full scale helis have to survive a power failure.