Hello Jim, nice to meet you.
I don't have any overwater experience with EGPWS, all I did at night on sea as co-pilot was something similar to ship-radar approaches, eye on radar-altimeter and CRM.
My opinion about EGPWS offshore capacity was based on logic: it is good on land (upon subject to emprovements to fit it to helicopter model), it may be good also on sea.
Understand you have different opinion based on specific experience and I do agree with you.
Maybe I should have write "..in overwater flying......I hope it would be as great as in mountains.", rather of "....I think......."
Sorry, maybe my writted lenguage is not as clear as it should be, I'm not mother thouge.
Maeroda