With the top of the front sight level with the top of the rear sight (and centered in the notch), the bullet impacts wherever the top of the front sight is placed on the target. There is some minor variation, of course, depending on ammo, distance, and shooter skill/vision, but I can use this alignment on virtually any Glock and hit COM out to 25 yards with the factory sight settings.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)