The blind fight feat is specific that it is "melee." Under the invisibility special ability, it mentions less:
A creature with the Blind-Fight feat has a better chance to hit an invisible creature. Roll the miss chance twice, and he misses only if both rolls indicate a miss. (Alternatively, make one 25% miss chance roll rather than two 50% miss chance rolls.)
However, it does mention this:
If an invisible creature strikes a character, the character struck still knows the location of the creature that struck him (until, of course, the invisible creature moves). The only exception is if the invisible creature has a reach greater than 5 feet. In this case, the struck character knows the general location of the creature but has not pinpointed the exact location.
Which makes me believe the intent is the within 5 feet - since a character with a reach weapon would be hidden more effectively.
Anyway - there's not a lot going for it either way, so any other opinions are welcome.