I completely forgot about Ray Anderson! And for that matter - two books from Verlinden.
And Joerg, you are right about about the two principles. Layout, design, telling a story, scenery, buildings, weathering are the basics. They are needed for any diorama whether it's a full scale museum piece or 28mm pieces depicting the farmhouse at Waterloo. Flats, I think, are more like the enclosed box diorama. There is a single point of view and there is a degree of forced perspective built into it - big pieces to the front, progressively smaller pieces to the rear, whether they were people, plants, or structures. Additionally, the ground should slope upwards towards the rear. Flats in an enclosed box would be the easiest (relatively speaking) versus a piece set into a shallow picture frame. Your pics illustrated these principles perfectly.
Cheers,
Glen