Today, I was using a 99 cent coupon for a medium ice coffee and the employee mistakingly gave me a small one. When I pointed this out, another employee took the small iced coffee, poured it into a medium cup with ice (enough ice so the medium cup was now full) and handed me the "medium" iced coffee. I looked at him incredulously (as did the others in line) and asked "That's it? Doesn't a medium iced coffee have more coffee than a small iced coffee?" No, he told me, they have the same amount of coffee.
I've been suspicious for a long time that I was being cheated by the amount of ice you put into the cups, but now I have proof. The only difference between a small, medium, and large iced coffee is the amount of ice! That's quite expensive ice I'm paying for when I get a large.
For now on, I'm buying a small iced coffee and asking for an empty large cup. I'll make the transfer myself and then ask for extra ice.