Request to share knowledge

My 5 month old baby girl gets very uncomfortable during bottle feeding. She is hungry and wants to drink but arches back while drinking. I don't think it's reflex cause there is absolutely no other symptoms of reflux but she strains and passes gas while drinking and this happens only when she drinks her bottle.

I am using Pigeon SS and nipple S is too fast for her. I tried pace feeding and burping as well. Tried many other nipples but she seems to be comfortable with Pigeon.

It will be really great for both of us if she is able to drink comfortably. Please share the tips that worked out for your babies or bottles or any other solutions. She is dropping percentiles and wants to drink but struggling. Thank you.