I've auto'd my HB Cool once or twice and while some will say it's impossible to auto a micro, but it just takes perfection to pull it off. I did one auto from about a hundred feet once when I thought the motor started to cut. Dropped the collective and headed for the ground maintaining rotor speed until at about 6-8 feet up I started to cushion the descent with cyclic and light coll pitch. That was all it took to bleed off the rotor and drop out of the sky. I would have done better waiting until one foot up to pull collective and cushion the fall. Not pretty but workable.

A too tight belt will rob rotor inertia and so will pulling in collective to arrest a descent. You want to keep wind going through the blades and that means dropping, not maintaining altitude when doing an auto with these little birds.