I'm not sure if it'd work, and even then I doubt you'd gain power if any. The 4FL curve already has more ignition advance, apart from the dip from 5-7000, which is below the powerband anyway. The 4FL has the pv controller inside the servo doesn't it? (three wires going to the servo means it is internal)
You would be better with a Zeel or ignitec which can be tweaked to be spot on.