Electrical load.
I understand that the generators are driven from the gearbox of each engine.
During autorotation what effect will a heavy electrical load (landing light, search light) have on the rotor rpm.
Could this be the reason the rotor blades rotational speed reduced below that expected by a very experienced captain resulting in a heavy landing.
I suspect very few pilots will have carried out autorotation to land with both engines shutdown.
Unless a descent is vertical the rad alt can be very misleading over a built up area as one can not be certain whether the return is from the ground or the top of a structure.
An easterly approach into JSY is a good example.