Well, there's too ways of looking at this.
If you want the easiest route to the best front handspring, put the board fairly far away, say between 2.5 and 3.5 feet out from the table. This forces the gymnast to stretch out during preflight and prevents them from piking.
HOWEVER, I DO NOT USE OR RECCOMEND THIS METHOD, and here's why: while a handspring from 3.5 feet out will likely be beautiful, a handspring front (or tsuk, or whatever else you want to throw) will be nearly impossible.
Putting the board that far out severely cuts their potential postflight power. If you want the highest and most powerful postflight, teach your gymnasts to vault with the board as close as reasonably possible. While this makes the preflight much more difficult and requires the gymnast to have a much faster heel drive, they'll find that once they get the hang of the faster entry, they'll have a lot more flight time after hitting the table. This gives them the time necessary for the more difficult upper-level vaults.
I'll use myself as an example; I am an elite floor/vault specialist, and I am, modesty aside, an extremely powerful vaulter. I am the first (and to date only) person EVER to do a tsuk arabian double front on vault. I'm about 5'6. I vault with the board at 2 ft; Any further and I can't get the height needed for the arabian double.
So, while learning a good-looking handspring is indeed easier with the board further away, I reccomend teaching it with the board close anyway.
I generally put the board between 1.25 and 2 ft for my students, depending on how tall they are, how fast they run, and how powerfully they can punch the board.