Ella, I have similar thoughts. DD has 6 7oz feeds per day - that's 42oz. She maybe leaves 2oz over the course of the day in waste. Usually she drains every bottle. So around 40oz too. (she is 20 weeks and 91st centile).
She feeds 3 hourly through the daytime and a dreamfeed: 8am-11am-2pm-5pm-8pm-11pm
She is just coming out of a growth spurt when she was waking in the night and was unsettled through the day. During that time I upped her bottles to 8oz and fed her more 2 to 2 1/2 hourly rather than 3 hourly. This meant she went up to 7 8oz feed = 56oz! 
I expect that in time I should be able to drop the dreamfeed so that she goes down to just 5 feeds in 24 hours and a more reasonable 35oz.
The SMA tin says 5 6oz feeds at 4 months (30oz) and 4 8oz feeds at 6 months (32oz). This may be where you saw the 32oz? I have never heard it being official though. The bottle size recommendations on the tin are just suggestions for the 'average' baby.
If I do anything to change this, I will put a scoop less of formula powder into every feed, but make them up to the same volume.
Also consider that there is some confusion about what defines an oz of formula milk (which sounds odd, but bear with me). I have always considered the total volume of a feed as the size of the feed. Bear in mind that what one person may call a 6oz feed (6 scoops of powder added to 6oz of water) I would call a 7oz feed (because the total volume of made-up formula is 7oz).