For a top down V neck incs are started at the beginning, most of the time on every 4th row. That ends up a couple inches above the underarms on me. If you want it higher than that, you would do them every other or every 3rd row. For a bottom up, begin the decs further up and also adjust the frequency to every other or every 3rd row. Remember that if you're going to put a neckband on, that's going to make the actual edge an inch higher too.
sue- knitting heretic