Transitioning targets

[IVC]

There are two separate issues here.

Yes, you concentrate on the front sight generally. If you want to hit a hard target, or if you need precision, it's always just the front sight. If you want fast shooting at close range, where sight misalignment is not an issue, you concentrate on the target (target focus). This is faster and it won't affect your score as long as the sights are reasonably aligned, as can be confirmed with blurry sights in the target focus aiming.

The second issue has nothing to do with sight/target focus, but with how you transition between targets. You can "ride the sights," where you keep your sights in view while you move the gun, or you can "snap your eyes to the next target," where you lose the sights and bring the gun in front of you to reacquire the target. This is faster, but harder. It requires correct "index" - the ability to get the gun to line up with your eyes. The reason it is faster is that you are not fishing for the sights as the gun recoils, you just drive it during the recoil - it doesn't go up-down-side, it goes sideways-up-sideways-down.

[SAD338]

This depends on the distance to the target. If the target is big, you can look through the sights with enough awareness of the front and rear sight alignment (i.e. frame the sights on the target) to achieve practical accuracy. If the target is small, you must pay attention to proper sight alignment.