Fulvio,
Not that I disagree with your post, but never has anyone been able to line up "3" objects with rion sights, only "2" will focus and the "3rd" will not be in focus, so therefore your front and rear sight should be in focus and the target blurred is the best but not the only option...For what its worth..

Most of my buffalo have been shot with my 450-400s or 470, all with irons..more than a few with bolt guns, some with scopes some not, mostly the 404 Jefferys..Im sorta of a nostalgic with guns and hunting.