Peep Angle Chart
You can choose between two peepsight angles, 37° and 45°. The angle of the peepsight is determined by the string angle and the horizontal line of sight. The decision, which angle is the one to choose, depends on three factors.
Braceheight, drawlength and ATA. The string angle depends on these three factors. In the ideal case, your should look through a peepsight with a full circle. If you see an elipse, you have chosen the wrong peepsight angle.
The table by Specialty Archery makes it easy to choose the right peepsight angle.