it's all about light. light through the sights and available ambient light.
I'm fooling with Palma/anchutz competition sights on a 223 right now. these sights have adjustable apertures front and rear. by adjusting the size of each aperture, it actually focuses the poa with the front sight. with the rear peep as close as functional or physically possible to your eye for a given rifle, you usually wind up with a ghost ring effect where you center the front sight in the rear ring with some daylight around the front. then center poa in the front sight.
That deals with light through the sights.
available ambient light will determine how big those apertures need to be, just like your eye's pupil, more light, smaller aperture.
the biggest hinderance to peeps is low light poa precision. That I don't have an answer for every situation.
testing your equipment in your environment is my only suggestion.
with the Williams peeps I run the .100" insert and remove it in low light using the threaded hole like a ghost ring.
I have found with consistent cheek weld and face position, the rear peep isn't as critical as you might think for reasonable accuracy. poa in the front sight is far more critical in my experience.
the attached pic is 2-4 rnd mags from a Tikka 223 @ 300 yds yesterday afternoon. That is the first group at 300 I've ever tried with a cf rifle too.
in my opinion, learning to use peeps accurately is a skill every serious shooter should master. I believe it is another way to build consistency.
I'm no master and have plenty to learn, I know just enough to be dangerous!