I'm sure there's a lot of sites of size out there in terrain you describe, like as not right under people's noses. If you look at the link to the aerial view that Baza's put up there are paths either side of the thing only a few feet away...walkers had been toing and froing oblivious. It is, imo, a good policy, used by the fieldwalker discoverer, and one I am using in my neck of the woods, to be holistic, ie, if there's a known settlement - in this instance Sittaford's hut circles - to look nearby for related features, such as burials/circles, and vice versa. Google Earth/Bing are of course useful, but definition, even with the publicly available lidar, means that getting out there and seeing in 3D is still tops. Time consuming, knackering and yes, maybe fruitless, but necessary. I've found something recently in an upland bog that's rather nice, will take a fair bit of work to fully expose and still have some peat prodding to do, that helps to make it worthwhile, but, yes, there is the urge on occasion to just go out for the day and snap and pat the known.. I haven't done that for weeks.