4 month old refusing bottle after 3/4oz

My little one has just turned 4 months and has started refusing the bottle sometimes after 3 or 4oz (she’s on 6oz every 3 hours) She’s been great with her feeding and how often she feeds every three hours has been guided by her, she always wakes and shows signs of hunger around the 3 hour mark but she will happily take a full bottle sometimes then refuse it after a few oz others, using aptamil and had no problems whatsoever so wondering if this is normal? The guide says she should be going up to 7oz about now but I feel it would be a waste of milk if she’s refusing some of the 6oz bottles! Some advice says up the teatsize/don’t worry about it/4 month regression but I’m just nervous she starts not sleeping through the night as she has done since 7 weeks old 😂 selfish I know! I just don’t want her to disturb her routine too much! Wondering if anyone has had this experience? Potentially thinking of doing 7oz but every 4 hours?x