It's more than just the type of sight, it also involves the "sight radius" - the distance between the sights. A short barreled gun with a shorter sight radiusis just that muchharderto shootas accurately atlonger distances.
Thelength of the barrels on hunting guns are a tradeoff between being light &handy and being toolong, heavy andunwieldy.A target gunwill usually alwayshave a longer sighting radius than a sporter/hunting rifle. A shorter sighting radius offers quicker target aquisition but is less forgivingwhen it comes tolong range sightingaccuracy.
Some of the precision targetshootersadda barrel extensionthat's like a false muzzleto increase their sighting radius and their sighting accuracy,plus their barrels areusuallylonger than a sporter barrel is to begin with.
Since the eye is only capable of focusing on one plane, and the rear sight, front sight, and target are all in separate planes, only one of those three planes can be in focus. Which plane is in focus depends on the type of sight, and one of the challenges to a shooter is to keep the focus on the correct plane to allow for best sight alignment. A tiny error in sight alignment can be multiplied hundreds or thousands of times by the time the projectile reaches the target; for example, with an Olympic-class air rifleshooter trying to hit the 10 ring, which is 10 mm in diameter, with a 4.5 mm diameter pellet at 10 meters, an error of 0.2 mm in sight alignment can mean a miss. At 1000 meters, that same 0.2 mm misalignment would be magnified 1500 times, giving an error of over 300 mm. (Calculations assume a 660 mm sight radius)
http://en.wikipedia.org/wiki/Iron_sight
I've usually heard that it's the front sight that should be kept in focus with open type sights, and to basically concentrate on keeping that steady while squeezing the trigger.