OK, I'm NOT and EXPERT, and I don't play one on TV...however, I am an NRA certified pistol instructor. This is the way we describe it (sight alignment and sight picture))in class:
Your eyes can only forus on one object at a time. If you doubt this, try the following experiment (taken from Jim Owen's book "Sight Alignment, Trigger Control, and the Big Lie":
With the sun or a strong light behind and above your shoulders, put your right hand at arm's length and down at a 45 degree angle with your index finger extended and the fingerprints facing you. Place your left elbow against your side and place your left hand in front of your body. (This gives the proper distance between fingers). Again extend the index finger with the print facing you. Make sure the finger on your left hand does not block the view of the finger on the right hand. The two fingers should be close together in the line of sight, positioned so you can see both at the same time. The fingers should be 10-12 inches apart.
Focus your vision on the finger closest to you until you can see the finger prints. You can still see the other finger, but you cannot see the prints. Shift your focus to the finger on the right hand and focus on the prints; you can still see the other finger, but you cannot see the prints. THE HUMAN EYE CANNOT FOCUS ON TWO OBJECTS AT DIFFERENT DISTANCES AT THE SAME TIME!!!
You can rapidly shift your focus from one finger to the other and convince yourself you are focusing on both -- YOU ARE NOT.
Ok, back to me. Having said that you can't focus on more than one thing at once, you do the following:
Focus on the rear sight.
Align the front and rear sights, shiftng the focus from rear to front sight. (technically, the sights are ALWAYS alinged with each other, but in this step you align the front and rear sights with your eye).
Focus on the target and raise the sights (in the same orientation) to the target.
Focus on the front sight.
Press (squeeze) the trigger.
Since the front sight is the last point of the bullet's travel that you can affect, it's imperative that you focus on it, and not other items. However, the other items do play a part, and the order, "rear sight, front sight, target, front sight" seems to have a great affect on shooting ability. If you have trouble focusing on the front sight because it's all black and devoid of features, draw a tiny line on it with chalk...and focus on the line.
Your rear sight does not degrade your accuracy. It's just a question of how to use it. It is used as a guide in which to bracket the front sight. Then your focus is on the front sight.
In order to become a better pistol shooter, you need to work on all the "fundamentals" (stance, grip, sight alignment, trigger control, breathing, and follow through)...not just sight picture/sight alignment. Again, I'm no expert...however, if you'd like to hear more about the fundamentals, e-mail me of contact the NRA...they can direct you to a local instructor.
BTW, I shoot IDPA too, and I've noticed that the front sight is all that's needed at close range, too. I'm convinced that enough practice with the same pistol would eventually get you familiar with your gun enough that sights would be unnecessary or "combat" use out to a great distance. Our head instructor can "point shoulder" shoot at 25 yds. and hit a Coke can every time.