Graviman
The 8-H-12 was use because it is one of the few airfoils that have been coded into my database.
Telling you that the use of FM is only practical when comparing similar rotors would be boring, because you have probably read it written by so many other rotor aerodynamicists.
However, let Leishman tell you in his own words: "Because the FM is a function of many interdependent parameters, it is only useful as a comparative quantity when using rotors of the same equivalent solidity and operating at the same disk loading; it cannot be used to compare efficiencies of substantially different types of rotors, a common error in its application."
Now that I have answered your questions, please answer mine above!
Dave