Headline News! I added another increase row and did more repeats before decreasing, which brought it up to the right size. I went ahead with paired decreases at each side of the stockinette sections, but kept the edge stitches for each section as k1 to make it smoother. I did the decreases in each cable row. At the tops of the stockinette sections, I did a ssk psso, but slipped the two knit stitches together to keep the central stitch on top. This gave a symmetrical look.
However, the final center decreases are not as nice as the way I did it the first time (on the right), so I will take out those last few rows and redo it one more time. But not right now. I just can’t frog things right after I knit them. Even those few rows.
Then there is still the brim to do, so this is still distinctly a work in progress, not a finished or even near-finished object. No rush.