I find wide pocket boards are awesome, when windy that is (10 knots and up)
Of course the width helps when you start and in transitions if you drop down - but that was not the question here as we talk full flight only.
I use the full width of mine - just found 4 kitecam shots to illustrate.
So no, you are not centered, far from in fact.
On a surfboard you will be centered, to be able to use your weight with both feet edging both ways, yes.
Not on a hydrofoil that does not turn the same way at all, no edge pressure - so stance is mostly personal preference I would think (strapless)
I stand quite open - way more comfortable and more room for turning, both when riding heel and toeside.
Sometimes I might stand fully centered too yes, but mostly open.
Two boards here, the Ketos Pocket 118 x 46 and 130 x 48 cm
Both more narrow at the rear where it is not needed, but at the front foot I think many of us like the open stance (apart from if open straps it has to be wide).
I think this is some reasons why they are so wide Jaros, and not as narrow as possible
118 x 46 and wavewing
130 x 48 and XL wavewing
So I dont stand centered, maybe others do I dont know...
PS: There is a thread about travel pocket boards, but we never got an answer what narrow and wide is according to the OP ? viewtopic.php?f=196&t=2397766