My DD has been on 4oz every 3-4 hours from 5 weeks until 12 weeks old and she is a very active 13.5lb baby, she sleeps well and can go for four hours in between feeds, and 8 hours at night, her small appetite hasn't affected her at all. Like us adults some babies are very hungry, others can take it or leave it some times. As long as it isnt effecting her sleep or her weight gain there is no need to worry.
Having said that ive started using fast flow this week and she now takes 6oz, But she is 13 weeks old and was getting very bored at feeding times as it took too long and too much effort, perhaps when your LO is a bit older you might change to a faster flow teat to see if it helps.