Feeding questions


So baby's ready to move to 6oz bottles. We usually full bottles with sterile water and then just add the powder as she's hungry.but once 3 scoops of formula is added to the 6oz of water it ups the volume n she's not going to drink it all. I know you are not supposed to alter water to formula ratio. Is premixed and poured into the bottles the only option? Its just so easy this way. We just keep the water in a bottle warmer and can mix up a bottle in seconds no waiting for it to heat up.