35 Whelen,
Read posts 15,17 and 19 in this thread. I'm one of those "seasoned high power competitor" people you're referencing.
If I put the front sight at the right side of the field of view seen through an aperture rear sight, that shot will go to the right of call. Took me a while to learn that when I started shooting. Then I learned to center that front sight in the rear one's aperture. I've shot my share of sub 12" groups at 600 yards with both post and aperture front sights.
When training a military team some years ago, this issue came up with the new shooters. I got a 24" long 2x4 with notches cut in both ends of the boards nailed at each end, put a match Garand barrel group in it then aligned its sights to have a perfect 6'o-clock hold on a 200-yard 13" black bullseye. Clamped it in place atop a bench. All the team looked through the aperture rear sight moving their head around in all directions noting the relative position of the blackened front sight post relative to the bullseye.
They all saw that the bullseye moved relative to the front sight; up with the eye up, left when left and so on all around the aperture. Only when the front sight was centered in the rear field of view did the sight picture have that "punkin on a fence post" perfect 6-o'clock hold.
Also proved that everyone looks through the sights the same; disproving that old myth that "everyone sees differently looking through sights which makes them all have different zeros for the same rifle and ammo." All have different zeros 'cause they each hold the rifle differently; bore axis points to different places when bullets exit.
Easiest way to see this is to put a finger on something steady about 2 feet in front of your eyes to represent a front sight. Then align your aiming eye to some distant object with your finger tip. Move your head around and you'll see that object appears to move left of your finger when you move your head to the left. That object represents where the barrel points on an axis between the target and front sight . Doesn't matter if you're looking through an aperture rear sight or not. Light rays travel the same from target to your aiming eye either way. If you align the front sight on the bullseye with it on the left side of the field of view through the aperture, that points the barrel too far to the left. Gotta move the rear sight right to correct for it in that left of center position.
Regarding sunlight striking front sight posts or beads. The old US Army Rifle Team's rule of thumb from over a century ago: "Light's right, sight right; light's left, sight left." Sunlight striking post front sights makes more of their sunny side easiest to see and that's what's centered in the rear sight. That makes the shot go away from the direction sunlight comes from. Bead front sights' typically have a bright sun spot on the side of the bead towards the sun. They need the same correction than post front sights do.
