4month old only taking 20oz formula per day

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My LG is 4 month old has been formula fed for 6 weeks, (stopped breastfeeding as latch never improved despite tongue tie revision). She has CMPA & reflux but both of these are under control on hypoallergenic formula with carobel to thicken. My issue is she only takes 20oz per day and has done since I started giving her bottles. If I try to give her more she cries and fights me. She will take between 1oz-5oz per feed never more than that. I’ve tried feeding her 2 hourly, stretching the feeds to 4 hourly and she will still only drink the same amount. We’ve changed bottles multiple times, teat size you name it. HV has told me she’s only taking half the amount she should for her weight. She’s 6.6kg and on the 50th percentile and has been since birth so weight gain is fine. She’s alert and happy the rest of the time. She has about 5/6 wet nappies per day but they are never sopping wet. Im a FTM and so worried about this but don’t see what else I can do, I don’t want to force feed her but I’m so upset after every feed worrying she’s not getting enough. Has anyone been through anything similar?