Really, this is what my knitting was telling me. I tried the edging from both sides of the shawl, k2tog, k2tog tbl, ssk; s1 purlwise, s1 knitwise; yif, yib... and it was still cross at me. Finally, once I got a chance to get into Borealis Yarns this Sunday, we have a winner. The first two repeats are ssk, s1 knitwise, yib (ugh! ugly!)... the last repeat is p2tog, s1 knitwise, yib. This zippers it up much more smoothly. I'm not going to think about whether a more obvious ridge is a design element - the ssk, s1 purlwise, yif was both neat and obvious, but any mistakes would have been glaring.