How low a descent rate do you claim to be able to achive in a A320 at a fixed speed (speed for max endurence) with both engines out?
Do it right and you can achieve zero descent rate for a short period in most aircraft, but probably not in an A320. The AOA protection would seem to prevent that. The trick during a ditching is to achieve zero descent rate at the moment your flight path intersects the water surface. Flare too soon and the descent rate will be high when the flight path intersects the water. As a P-3 pilot we practiced ditching in the simulator and a hundred or so feet above the water fairly routinely.