"Small", "medium", and "large" are all relative. A level maker can tag their level with whatever size they want, regardless of actual size, and many (most?) levels do not have size tags at all. The difficulty, too, is subjective. And level genre. You'd need a three-dimensional graph to sort out all the different possibilities.
KS levels simply are not standardized (and can not be standardized) to a degree where some score incorporating multiple levels would be meaningful.