I know you like the feed you're providing but when you say they're picking out what they like, It reminds me of when I used a feed with alot of grains like Mile Four layer feed. They did the same thing, picked out what they liked and left quite a bit behind. And eventually I saw via the dull color of their combs that nutrition was an issue.You kind of have nothing to lose to try making changes like a different feed. It's not going to hurt them at any rate. I use a shaker can too when I need to get them in but it's not nightly. I have a light in my coop so that when the sun starts to go down, the coop is the preferred option. There is nothing wrong with herbs in nest boxes. I use herbs, dried flowers and essential oil all over my coop. I'm thinking the main point there was fake eggs. Definitely try that as well as enlarging boxes if they're too small.