I ripped out the collar and neckband, picked up fewer stitches along the saddles and back neck, and reknit a narrower collar — narrower by almost the width of the button bands to be added.
I will have to give up on the option to wear the collar buttoned up all the way and loosely folded over, but I’m much more likely to wear the collar open, and it will look more balanced this way. Picking up fewer stitches also gives a closer fit around the neck and I the necline did not pucker as I had feared.