It'll be slightly less detailed, but a good portion of it still needs to be on the mesh, considering that the player will likely be flying rather close to these things and that's where normal mapping breaks down a bit, especially if you're trying to capitalize on TRD, skimming over the trench or terraces. Looking straight down'll kind of break immersion when you notice it's actually flat. Parralax mapping will help with that, however, but there still needs to be significant detail on the mesh itself. Remember that many of those little greeble bumps are still as big as a whole fighter