Hi there, I would def try for the 3.5 hr EASY, and if this does not change things, then you may just have to go with the flow, he may just be a baby who does not drink LOADS of milk, 20-30oz is respectable, and there is a wide range of normal. It sounds like he is doing great as you said, so I wouldnt worry.
Try 3.5 hours between feeds if he can do it, and see how it goes