6 Week Old Formula Feeding Too Frequently?

My 6 week old formula-fed son is still wanting to eat every two hours around the clock. My pediatrician told me to continue to feed on demand at this age, but he’s in the 75th percentile for his weight and only the 35th percentile for his height and head circumference. I’ve tried to stretch his feedings but there’s literally nothing that soothes him until he gets a bottle. This has been the schedule for a while and he’s never went longer than this to eat, so I don’t believe it’s a growth spurt. He’s eating 3-4 ounces at every feeding, usually closer to 4.

Is this normal, should I continue feeding on demand and if not, is there a way I can start to stretch his feedings out?