I have tried a few different sizes and I measured my nipped with a measuring thing, the pump has 3 modes and 12 suctions strengths and I have to have it in max at 12 to do anything
Also yes it’s silicon I think, my friend has the same pump and she finds it empty’s her okay but she doesn’t have elastic nipples, I use a 24mm on my electric which I find comfortable and pain free
You might need to change the flange size on the hands free pump. Which flange size are you using? Are you using silicon flanges in the bands free pump?