Hi there
Honestly I am not great with bottle feeding advice but I saw you didn't have a reply yet so thought I'd stop by.
Do you feel your LO is fully ready for the 4hr E routine? There are some babies who need to eat more frequently in the day than this, mine was one of them, he couldn't go longer than 3hrs between milk feeds until he was 6 months old when it naturally extended due to naps and solids times.
I just wonder if your Lo might do better on 3hr or 3hr 30 feeds in the day to get his calories in and not need the 3 feeds over night. Tummies are very small and for a small baby the tummy is even smaller. Mine was a petite boy and also reflux meant he preferred smaller meals more frequently.
Intake can dramatically increase during growth spurts and us parents can get used to that amount being taken so we can be shocked and worried when the amount drops back to normal - could this be the case? I do remember being astounded how much my DS took during a GS but then did worry a bit when it dropped again.