Flange size

If your nipple is rubbed against on the flange, it means the falnge doesn't suit you. Just get one size bigger maybe 21mm instead. When u just started to pump, the nipple is small and after 10mina the nipple will get bigger and bigger and hence it it alright to use falnge is slightly bigger as long as the nipple doesn't rub on the flange

the pump I know mostly size 24, 28, 30 what pump did u use? last time I use medela flange size 24 and I have no issue with it. My friend bought haenim and she say she can use size 24 without the padding or size 28 with the padding. Maybe u should try another size or another pump, the expression power might be different for each brand