I have hardwired myself to acknowledge every time aloud for rear crew to hear and state overwater
This is the secret! Though I have never flown a retractable helicopter, I have done a lot of amphibian airplane training. Regardless of whatever (if any) gear position warning system, I insist that the pilot state the surface for the intended landing, and the gear position observed. This extends to wheels skis (which work poorly on hard surfaced dry runways, and even for regular RG landplanes, if you're thinking to ditch: "wheels are up for ditching is a possible correct call out"! Flying can have distractions, you gotta get yourself out of the distraction for a moment for each landing, just to assure configuration.