When you look down, you should see his side and his mouth should be covering at least a half - inch of the dark area around your nipple. (pregnancy-info.net)
The base of your breast, about a one inch area around the nipple should be in the baby's mouth with nose nearly touching the breast. (thebabycorner.com)
If the flange is too large, you will see your areola (the brown area around the nipple) be drawn into the flange. (cindyandjana.com)