Exactly how big an object should you be able to see when you have a visibility of 1 mile, or 5 miles, or any distance? What can be seen 5 miles away? A mountain? The moon? A water tower? What?
Well, if you are talking about horizontal visibility, then you have to consider the curvature of the earth. If you were standing on a ‘flat’ plane somewhere on earth your horizon is about 3-4 miles away. As you go higher up you can see further round the earth of course.
That being said, I cant quite understand the rest of your question.
At 400 yards, a human target on a shooting range, is pretty damn small. Looking around me now, and on this camp we have visibility points everywhere for ascertainling the meteorological visibility, I can just make out a person at about 3/4 of a mile.
Depends how good your eyesight is though.
If you look up in the sky, you can make out airliners flying at 30,000 ft (approx 6 miles).
Individual trees are visible on ridges 5 miles away or so.
As long as the meteorological visiblilty allows it, you could see a high mountain from many miles away, perhaps up to a hundred miles.
High meteorological visiblilites in the UK, would be about 40 miles plus, though in other parts of the world the air is purer and the visibility further.
At a previous base I was at, one of our visibility points was a ‘white horse’ hillcut figure, which was over 20 miles away, and that could be just about seen for what it was.
Dont really think I’v answered your question here, but there ya go.