I have peep issues.
I got more peeps than arrows thanks to specialty peeps.
different lighting, change peep.... dark 3D course, change peep...light 3d course,change peep.....target round, change peep....change scope power, change peep....ect....
As a rule,the better the lighting the smaller the peep I use.
And I am always changing scope power for different games so that changes my peep too.
Not really much help but peep size is kind of a trail and error thing with a lot of personal preferance thrown in.