I think what GP is saying is if you zoom to the max level 15 there remain only 12 cells which come out as pentagons and all 12 of those are in the ocean (albeit

I think what GP is saying is if you zoom to the max level 15 there remain only 12 cells which come out as pentagons and all 12 of those are in the ocean (albeit sometimes very near shore). If you zoom to the global scale those 12 get inherited into ever larger parent cells which do cover large areas of the Earth though, as you found.