Good question...and I think it depends on the situation.
I've often heard it said that you should not paddle past your feet..and yet every day I look down an see my paddle stroke almost as far past my feet as I reach in front.
I've heard it said that paddling past your feet sinks the tail of the board..but if you have a large thick board like the 11'6" Naish there is not going to be any tail sinking going on..

..I don't think.
I think it depends if you are accelerating or sprinting..vs..cruising along.
When I am accelerating I tend to use short quick strokes that stop at about my feet before reaching forward again..but once up to speed I tend to slow down the strokes and start stroking longer..and well past my feet before reaching forward again.
It may also depend on the board..and your paddle length..maybe even body shape...even if paddling into the wind or downwinding..There are a lot of variables.
I think it comes down to what works for you..and with heaps of time on the water you will create your own technique and style.
That's my two cents worth..I'm sure others must have their own thought on this.
DJ
also..This youtube vid of myself on my old NSP board shows what I mean..I don't claim this to be the correct technique..I did it so I could get advise on what I'm doing right or wrong.