IMHO, you are severely handicapped with your choice of the folding leaf rear sight. The notch in the slider is so small that holding the bead centered will be difficult. These sights are found in many applications, but they are a poor, difficult to use choice.
The human eye cannot focus more than one object at a given distance distance at one time, so shooters discovered that the peep sight rear and flat top post front sight provides the best sighting arrangement short of a scope which places the aiming reticle and the target on a single sighting plane. The thin rim large aperture (ghost ring) rear sight is the fastest for practical field shooting and the large rim small aperture is the most precise for the target shooter. The rear sight is ignored, you look through it not at it, put your front sight on the target, then pull your focus back to the front sight and hold it there until you break the shot. The rear sight has blurred out of focus, the target has blurred out of focus and only the front sight is in clear sharp focus. To see how this works hold up the index finger of both hands so they are both in your view, place one about a foot from your eye and the other at arms length. Focus on the fingerprint of the close finger, when you do that the farther finger is out of focus. When you focus on the far finger so that you can see the finger print, the close finger is out of focus. Now find a point on the wall, and focus on it, and you will see that both fingers are out of focus, but you can shift your focus so that any one of the 3 is in focus.
A post front sight provides an index of elevation that a bead type front sight does not. Think of a post front sight like a cross hair. The flat top of the post is your horizontal wire and the center of the post is the vertical wire. The human eye is very good at finding the center of a front post.
If you still prefer the idea of a V notch sight and a bead front sight (metallic or fiber optic), you should choose a wide V sight as is typified by the express sights often found on dangerous game rifles. When the height of the rear sight is regulated to the height of the front sight, it provides the fastest line up with this type of sight. The bead naturally drops to the center of the wide V and it is easier to hold the bead centered in a wide V than in a narrow V or a small U notch.
