Pound for pound applies to all wieght classes.
It has to do with the ratio of skill per pound. If you have a certain amount of skill per pound, ratio will be constant whether your 100 pounds or 200 pounds.
In high school, they kept records of all the students in wieght lifting class. The strongest guy pound for pound was this big guy who was over 200 pounds. You can just divide the amount you lift by your body wieght to see how much of your body wieght you can lift.
It's not as accurate in fighting as it is in weight lifting becuase it's based slightly on opinion in fighting.
And midgets tend to be very strong p4p in bench press.
But sometimes even wieght lifting p4p is inaccurate becuase, some people will cheat by letting their legs get skinny and small, so they weigh less, then they will get their arms strong and have a very good p4p bench press.
I had always been under the impression that "pound for pound" meant who would win in a game of no-limit bloody knuckles. Color me embarressed.