Target visibility

[6S.Tamat]

Tomcat Insuber is right; for the sight range see the documents that we found about it wrote by the U.S. Navy.
As simple example i would remember you that a runway of an international airport is from 1,6 nautical miles (3000 m) and 2,2 nautical miles (4000 m).
If for seeing a contact with for example the sun behind your back you need to barely enter in formation with him we are really unlucky without radar..
About the contact visualization of moving objects it is simpler, cause the human brain (and of the animal in general) is made for enlight the moving objects.
But i need to say that the image that you posted is really interesting because add to the discussion something that we lacked: info about the contact seeing in one of the worst situations, the one with the sun behind the contact.