What you are talking about is Leupold's generous eye box. One of the major reasons why I'm such a big fan of Leupold rifle scopes.
The other advantage of their long eye relief is that it's easier to mount the scope and algin it with a moving target because the further the eye is back from the scope, the easier it is for the eyes to see around the scope.
Not all Leupolds are built this way, however. I've got a 3-9X33 Compact that has no better eye box than the 3-9X40 Zeiss Conquest, for instance. And my old 7.5XAO has no where near either the eye box or eye relief of the 6X42 the rifle also uses. E
