I find this interesting from a statistical stand point. Hypothetically speaking, your chance of failure increases proportionally to the more you collect. Say you want all four. The first box you get will have a 100% chance of getting a character you want, the next will have a 75% percent chance, the third will have a 50% chance, and the fourth will have a 25%, assuming all other factors are equal. The likelihood of getting all four on your first try is 0.09375 or 9.375%. The two events are independent in regards to how they are arranged, because the amount of minis is not affected by which ones you buy, but by which ones you want.
Also, normally you can check the serial number to see which one is in what, but where's the fun in that?
(Yes, AP Stats has conditioned me to look at something like this and think about it through this lens)