I don't think it really matters where you pick up these sts as long as you're close to the seam line and to the neck edge of the sweater. Really this technique is very forgiving. Here's an example
on a straight edge. You may even be able to skip these instruction and just work with the neck sts from the fronts and back without the extra picked up sts.
You might also give this a try with knit swatch and some scrap yarn so that you don't wear out your good yarn. See if this video
helps. It doesn't really show the pick up of sts over the seam but I couldn't find one that shows that part.