Pistols no problem. Rear aperture on a military rifle? I get dang "line" in my sight picture. No matter the diameter of the aperture. It slices my sight picture like a prism so I have to "decide" which target I'm going to shoot. I am shooting master scores but I think with a clear sight picture I could do better. I have scratches on both right and left lenses.
I have had a "cracked lens" line with peep sights for 10+ years. You are the first person I have run across that has experienced it as well. It is the reason there is a red dot on my Garand. It is a shame, cause I shot irons very well for more than 40 years.
With pistol sights, I can see the front sight or the target, not both.