formula feed before/after nap??

so i switched from combi feeding to formula feeding about a month ago. she usually takes 5 bottles a day, ranging from between 5 and 7oz at a time (usually 6ish). up until recently i've been feeding her when she wakes up from a nap - i started doing this ages ago to try and avoid her falling asleep while feeding / feeding to sleep. but now her wake windows are getting longer - although she does sometimes nap for an hour, more often than not it ends up being 30-40 mins and i'm wondering whether she's waking up hungry.. how much formula should i be offering her before a nap and should i offer before every nap? just conscious that i don't want to overfeed!