It would have been nice if they could have had a +1, 0, and -1 foot levels in the game, and then, while we're at it - tides!... lol - Look at Apo Reef (I think), and it's got the west part as shallows, but is missing the east part. Ah well.
One thing you might run into with using the Environmental is that they don't (can't??) take damage, so you'll have a time "registering" mission completed on the shelling part of it...