Where does your guitar should be hanging? High or low?

I've seen guys like:

James Heatfield (Knee low guitar, plays rythm)
Nuno Bettencourt (great shred at pretty low altittude)
Zack Wilde (low guitar shredder)

All of the above play with their isntrument strapped pretty damn low

Now for example, (everybody bow down your heads)...

John Petrucci, he plays with his guitar so high...

I mean in technicwise I found that higher is better for me (is more relaxed), I can pick faster and fret better, but I think I have a problem cause I practice a lot sitting and when I stand up I found trouble playing with the same quality.

Is this a matter of getting used to it?, Arm lenght?, the way you arc your fretting hand? finger lenght?

Any ideas bout this?