I'd do what Pumpkin suggested. I've been following your other thread so I know you had good results/insights with the feeding ultrasound and the expressing after feeds while he readjusts to feeding after the procedure so I really think you are doing wonderfully and feeding more often will really work to kick the comps out the door. Can I ask how often he feeds day and night? And how much do you express roughly after each feed? Do you feed him the expressed milk? Can you do that instead - comping with EBM instead of formula? DD lost over 10% of her birthweight too and one midwife pressured us to comp feed but I refused and just offered my boobs all the time and expressed like you are doing. We didn't have alertness/nappy issues though. So yeah, keep doing what you are doing, you sound like you are already achieving great milestones with him, but don't be afraid to drop the (formula) top ups once you are expressing enough and/or babe has learned to suck effectively.

Maybe Barb Glare might drop in with some professional thoughts too.