Extending the sight till you see archers would be a little too much, and it may well kill the archer's advantage on long range.
It would make much sense if the longer sight came with the second defense upgrade cause "arrow tower" should in theory = "longer sight".
Maybe increase the sight x1.5?
It's just to give you some feeling of the surroundings, and not make you have a total palantir-like vision all over the map. the scout units, and sight spells should be meaningful after all.