The conventional wisdom is that the larger packages will be cheaper per unit. Usually they are, but not always.
I've noticed this a lot with ketchup. We always buy Heinz (except during a brief period in 2004, I can't recall why ) and medium-sized bottles are frequently less expensive per oz. than some of the larger sizes. Luckily, Kroger does show unit (e.g. per oz) pricing on most items, so one just has to remember to look.