My first welt was loose, too. But Welt No. 2 was when I found religion on how to pick up the welt-making stitches that happen in Row 7 of the Silk Cloud. I'm kind of stoked about this, and if I get organized, I'll make a video.
Here's what I did:
The problem for me with Welt No. 1 was that I was looking over at the wrong side of the work to find and pick up the correct purl bump. I had no way of being sure that the stitch I was picking up was in fact the correct stitch, six rows directly under the stitch on my needle that it would be knitted with. If you pick up the wrong stitch, you can end up with a slanted welt. OH MAH GAH THE HORROR.
My solution: stop looking at the wrong side of my cowl to pick up that stitch. Instead, I keep right side facing. I look at the stitch on the left needle, eyeball down six rows, then—without looking at the wrong side—I stick my right needle from the wrong side into that stitch six rows down. I catch the top of that stitch with my right needle, pulling it back and upward, and place it on the left needle. Then I knit the two stitches together.
With this method, I can confirm that I've got the correct stitch picked out before I knit anything. And it's faster for me, too. Maybe you guys are already doing this. But I was so happy to not be looking at the wrong side anymore.