Sight Radius
Something else to keep in mind is Sight Radius.
I have a Williams peep on my Camp 9. It adds something like 8 or 10 inches to the sight radius. That alone, without further optical advantage, improves accuracy. Juice bottle caps at 50 yards.
Permit me to grab some imaginary numbers out of thin air.
It's simple geometry, really. If your front-to-rear sight "slop" is, oh, let's say a half-millimeter (for argument's sake), and your rear sight is on the barrel forward of the receiver, the slop at 50 yards is going to be (again, let's say) 2 MOA.
You have a pair of "similar triangles" that share a vertex, the smaller of which has a half-millimeter base and two 16-inch sides, and the larger of which has ~50 yard sides and a proportionately wider base.
Anything you can do to narrow the angle of that vertex improves your accuracy. There are two things available: 1) narrow the width of the "slop" base (diopter peep), or 2) lengthen the longer sides of the smaller triangle.
Moving the rear sight back another eight or ten inches reduces the angle of the shared vertex, moving the "slop zone" at the target in from (let us say) 2 MOA to 1.5 MOA or whatever.
Someone with a calculator handy and a ruler to measure the actual apertures of the sights can come up with hard numbers, but just a crude drawing on paper will demonstrate the principle.
Even if you use a larger "ghost ring" for the rear sight, the longer sight radius is going to help a lot.
A receiver-mounted peep will give you several inches more on the "legs" of your shooter-side triangle, while a tang-mounted vernier peep adds even more length.
