I always wondered that myself. I like to keep it at a distance where when I look through my peep sight I can see the outer ring (my cobra has a orange ring) of my site. So if I am looking through peep sight the orange circle is just on the inside edge of my peep. But would like to know if a longer one is better also.

Kind of a crude pic ( I think the string needs some wax..)
crutch
Opps .... for got my pic