Hi Si
Not sure I agree with Moose... sorry Moose - no offense. Although what Moose says will probably get the job done,
What Moose is saying is correct in so far as you need to pick a distance to base your peep setting on. You can't just open your eyes, line it up and go. It will be right for wherever you have the sight at the time but will be a compromise in terms of anchor point at all the other sight positions.
Most people find 70 a good starting position. I find that makes me a bit floaty at 90 so I set mine a bit tighter. Id rather be solid at 90 and a bit compromised at 30 as I'll lose less points that way. If I'm only shooting one distance then I'll set it for that distance obviously.
How much of a compromise you'll have to make will depend on the speed of the bow and how far the peep is from your eye. A slow bow with a tiny string angle being the worst, in my experience.
With all this in mind, despite having a 30" draw and shooting 60lbs, I can sometimes struggle to get a good sight mark for 90m with some bows, whilst maintaining good form.
As with everything in this game it's never black and white