Short version:
Present pistol to target. Quickly verify that front sight is on target. Pull trigger.
Slightly longer version:
The reason you're only glancing at the front sight is because, at close enough ranges, sight alignment, and your consequent ability to make acceptable hits, is virtually automatic. This is the result of ingrained muscle memory developed through basic marksmanship practice.
In other words, when you present the pistol to the target -- having already established and practiced good basic form -- you're merely verifying that the sight picture is “good enough” to put rounds into an eight-inch circle. Why an eight-inch circle? Because that's a useful standard of “good enough” combat accuracy -- at least according to those who study and write about such things -- and it can be achieved by giving the front sight due attention. That's because it's the front sight that's prone wander out of place. Not the rear sight. You bring the pistol to your eyeline the same way every time, whether you look at the sights or not, the sight picture should be in the ballpark of acceptable. At close enough ranges, the rear sight becomes merely an incidental window through which you see the more important front sight.
So if you present pistol to target and that front sight lands in your aiming area, a clean trigger pull should put a round acceptably on target.
As the distance to the target increases, or the need for precision becomes greater, you pay much more attention to sight alignment and the relation of that sight picture to the target. At long range, a slight displacement of front and rear sights produces a larger error. At closer ranges, precise sight alignment isn't necessary to make acceptable hits, and trying to get a precise sight picture slows things down.
“Front sight” aiming, aka the “flash sight picture,” is a good, useful, repeatable way to achieve good hits at reasonable speed.
