The rearsight should be blurred.
The foresight should be in focus.
The target shouldn't be in focus,you shouldn't be able to see detail to aim at "a spot" on the target, the black centre should be a blurred round dot hovering above your foresight - you aquire a consistant target picture that looks like this -

http://www.jarviser.co.uk/hawc/image...ht_picture.png

If you're trying to see detail on the target you're doing it all wrong
ATB,
Nick