High mob farm over land vs over ocean

So I am planning to build a mob farm on a survival server. I intend on building it very high up. I was wondering if I should build it over the ocean or over land. I know mobs spawn better over an ocean because they can't spawn in the water, but what if I build it very high up over land? Is the efficiency the same for a mob farm built very high up over land and a mob farm build high over an ocean?

This is the type of mob farm I intend on building, (the image is from google I havn't built mine yet)