This is an old post, but you could see how this extension is doing, or do other searches in the forum about importing data:
With the built in Digital Globe and Nearmap, the terrain data comes from someone else, and it’s the same source for both tile image providers.
I think that it isn’t just being 18X, but also selecting the smallest area. I’m going to test that on a hilly area, to see what level of detail I get.