with olivia we had such a huge range of Df amounts but it seemed that little extra is what helped her sleep through - sometimes she took as little as 2 oz her average was 3-4 oz and occassionally she has taken 6-7 oz. we found that once she was sleeping through the night regularly as long as she had 4 oz she would sleep til almost 7, on nights when she took 2-3 oz she would generally wake at 6:15 - 6:30 so although it seems like a waste, every little bit helps some babies.
we have become so reliant on the Df though that we are only now trying to do without it - she is sleeping through the night still but yesterday woke at 5:45 and today 6:15 so i am praying at almost 9 mo we can finally call it a night
at 7:30pm instead of 10-10:30
also - we never worried if she woke during the Df as she woudl go right back to sleep (only worry if you have a lo who wil wake up and then be up for ages with you struggling to resettle) - also know that they can go through a period where they wake before the DF looking for food - i woudl just feed them and if they take a good amount don't worry. if let's say they only take 2 oz at 9pm we found we could then go in before bed around 10:30 and just top her up with a 2nd DF and she would take another 2-4 oz