Here's a picture to introduce the problem and its simple solution:
This comes from a reddit thread named "How peep sights look IRL and how they should look in game", which refers to the game RS2 Vietnam, yet it covers the exact same issue present here and in many other games.
It is worth remaking how popular addons for ArmA 3, such as RHS, have correctly implemented a blurry rear aperture ring on the M1 Garand. This in my experience, provides the possible best adaptation of reality's own "Mk1 Eyeball" and its usage in combat within the context of a 3d simulation renderer.
The result in ArmA looks like this (M1 by RHS):
This seemingly trivial detail really plays a very large role in the process of target acquisition. With a hard and opaque rear aperture, a small-ish target becomes wholly obscured when traversing one's aim onto it. This "Blind Zone" around the center reticle is not an issue with a physical eyeball or camera lens due to Depth of Field effects.
While ArmA does offer a DoF effect, the results of it are less than ideal and most importantly, there is a noticeable performance cost attached to using post-processing as such. For some of us with hardware of a more "pedestrian" grade, the FPS toll is quite prohibitive.
Therefore, I believe this simple adjustment would prove a great quality-of-life improvement for us G.I.s out in the field, especially when dealing with quick moving targets so adept of playing "Hide and Seek" as Charlie often is.
Cheers and thanks again for an awesome mod!