I am one who does demand feeding. I don't have a baby on formula right now but my youngest is only 20 months so it's still recent memory. All of my kids but my youngest went to follow up formula at 6 months. They drank 6oz at a sitting. My youngest one was FTT so his feeding schedule was all over the place. I fed them when they wanted to be fed. They all slept through the night and that is another highly individual thing. My youngest will only nap for 45 minutes but my 3 year old still naps for 2-3 hours. He has also always been a long night sleeper. I would say, if your child seems ok during the day from sleeping that long at night, then that is just his internal clock working like it should.
All of my kids started out on 2oz, then 4oz, up to 6oz, and eventually to the full 8oz. I would think it would be natural for him to go longer between feedings but eat more at each feeding at this age. The best thing to go on is your baby. If he seems content with the way things are going, I would stick with it. You might want to try a day of going longer but feeding more. If he is happy that way too, go for it