Landing across the swell (along the length of a wave) is supposed to be smoother and should prevent a nose-down surf into a wave trough.
Manufacturer's ditching advice for the S-70 as I recall, (no floats on ours then), is to deliberately roll the aircraft over (to the right?) in a positive and controlled fashion before the rotor slows to the point where it's no longer flying.
I think this is to make events more predictable than if the rotor is left to it's own devices in the final few moments. The drag of the water will stop the rotor very quickly so the next part, the crew evacuation, can begin asap before the aircraft sinks too deep.