For proper sight alignment the top of the front sight is even with the top of the rear sight, and there should be equal spacing separating the front sight from the sides of the rear sight.
The eye can only focus on one object at a time. It cannot keep the rear sight, the front sight and target in focus at the same time. The shooter must concentrate on the front sight. The front sight should appear sharp and clear, the rear sight should look less sharp, and the target should look blurred.
For example, think of your self driving down the road and a rather large bug smashes onto your windshield, your focus immediately changes from looking down the road to the bug. Even though your looking at this mess you can still see down the road, blurry though it is but workable. Same with looking at your front sight, it must remain clear and sharp. Without concentrating on the front sight you will never know where your shot will go on your target.