Has Anyone Else Noticed This?

Because I live alone, I tend not to buy very many things in bulk, but there are a few exceptions.  For example, laundry detergent.  It's generally been my habit to go with the biggest box I can find, just so I don't have to restock very often.  Another factor is that-- I always assumed-- it was cheaper to buy the big box, since there's normally a bit of a discount (per ounce) when you go with the economy size.  But yesterday I was in the store, needed to restock, and actually checked to see if this assumption was true or not, and to my surprise, it wasn't.  It turned out, in fact, that the smallest box was the bargain, saving me around fifty or sixty cents over buying the larger packaging (I bought several of the small boxes to equal the amount of the larger size, so I still won't need to purchase it again for awhile).  This seemed to fly in the face of the common knowledge that bigger is cheaper, so I decided to check another product I tend to buy in the bigger size: orange juice.  I generally buy the gallon jug of Minute Maid orange juice, but it turned out in this case too, that it was cheaper (by about twenty cents) to buy two half-gallon cartons.  Just out of curiosity, I stopped at a different store to see if the pattern was repeated there, and in the case of these two products, it was.  Granted this is a small sample size, but it makes me wonder if retailers have spent the past several decades training us consumers to always go for the bigger package, anticipating economies of scale, only to start jacking up the prices on those portions once we started to do so without actually checking. Is it possible that manufacturers and retailers have pulled off the old bait and switch on us consumers? I'd be curious if anyone else has noticed this trend.