Blues harmonica? Country harmonica? Old time/traditional folk harmonica? Tremolo tuned or not?
 
All sound different and require different techniques.
 
As a general principle though, harmonicas are much louder close up then you'd think and can overdrive many microphones without a bit of distance (though blues harp in particular relies on overdrive). They also tend to lack bottom end and have a big upper mid spike, especially if tremolo tuned. If playing into a guitar amp it's usual to have to reduce the treble a lot and boost the bass.
 
I consider distance miced harmonicas as essentially a woodwind instrument. Close micing gives more of a "Chicago" sound and hand cupping/uncupping doesn't have anything like as dramatic effect as when using a more distant mic.