A high functioning person (normal or otherwise) would, to me, be someone like Sir Winston Churchill who was reported to need only a few hours sleep a night and got England through the Second World War. Or someone like Sir Richard Branson or Margaret Thatcher or the like. I would include any normal person with those patterns if living including owners if businesses who work 20 hours a day and still make time for family on Sunday or the single mother that has 2 kids and works 3 jobs or the disabled person who devotes their time to caring for other sand helping their community etc.
So I think high functioning can be seen as an entity by itself. In that way one of the examples above might be an alcoholic in which case they would be a high functioning alcoholic. However if the alcoholic is not doing anything extraordinary other that running a home, got a family and a job then I would definitely consider them a functioning alcoholic...possibly.
The High part of HFA just leaves a bit of a rub because I can imagine myself saying that when I was drinking with pride. Also my idea of holding down a job, having a family and keeping a home whilst claiming to be a HFA would have been ok whilst drinking but then at some point I would have sobered up and learned that functioning takes on a whole other meaning when applied to me by other people.