Pump ? - Flange size

kimikins79

I have a variety of flange sizes for my Ameda PYU pump.  What is normal - my nipple and a large part of my areola are pulled into the flange when pumping.  I know we have to stimulate the areola to produce the milk, but how much?  It looks "odd."  I am just not sure what size to use and I have tried various ones.  It seems like the position of my nipple in the flange is what produces "different" amounts of milk expression and/or stimulates a let down.

Does any of this make sense?  Any help is appreciated.  I want to make sure I am pumping effectively.