I was just thinking about this the other day. I used to think it would hurt less to have a smaller baby. I had an almost 10 pound baby drug free and sure it hurt. I tore but I think that was because of positions (I was on birthing stool and he was on an angle).

But what is the pain from? Contractions- you're going to get those regardless of the size of your baby and Crowning- pushing a lemon out would hurt so a 20cm, 30cm, whatever head is really not going to feel all that different. So all birth can feel the same regardless of the size of the baby. I would agree that bigger variants to pain would be the mother's mental state, position of the baby, position of the mother etc.