LOL Had just told my son this very thing 30 seconds before I saw your post. Smaller boxes of whatever are usually on the top or bottom shelves. Larger boxes are eye level. People usually buy what is in front of then.
Years ago I worked in a store similiar to WalMart before WallyWorld even existed. Smaller item went on the left, larger on the right. Most people are right handed and tend to stand right in front of whatever product. They would normally reach for the size on the right. Off brands (cheaper price) were on the bottom or across the aisle from the name brands.
Yup.
Cereal aisle: Kids cereal on low shelves at kid eye level. Adult cereals up high. It's called marketing and presentation. People are sheep.