I think the reason he isn't sleeping very well in the day is that your A times are too long so he is getting overtired (OT). At 6 weeks his A time should be around and hour, maybe 10/15 mins more and that time includes the feed time (awake time rather than activity, eyes open to eyes shut). If he naps less than 1.5 hours you need to shorten the next A time or he will get even more OT.
Have a look at this link -
chronological EASY samples, 0-3 monthsHave you got a sleepy time routine yet for him? Is he only having one nightfeed? That's great if he is! What's his night sleep like, is he sleeping soundly between bedtime, feed and wake up?
With the feeds, I would say he is probably still snacking really. The way to tackle it is to feed him, stop at about the 20 min mark and then leave him as long as possible until the next feed. You don't want him to get distressed but distract however you can to get as long as you can until you feed again. He should take a better feed as he will be a bit hungrier, next you keep the next feed at least the same time scale apart and stretch for another 5 mins if you can. He should be able to do at least 2.5 hours between feeds on formula.
With my DD we did some formula feeds and some breastmilk feeds for the first week or so of her life. She was taking 3oz a feed at that point and would last 3 hours if it was formula but be hungry at the 2 hour mark if it was breast milk. By 6 weeks she was taking a good 5oz at a feed.
Laura