Very interesting technique !!!
The feeling of depth is well given by the back painting on the three dios.... It gives good ideas of the theme.
I never practiced dioramas, because the background often tends to dilute considerably the visibility of the characters on the front and distracts these subjects, as all are coloured with an equivalent intensity (value) of the tones.
But by using lighter colours, or even black and white tones ("grisaille") to give the contrast of the front paintings that are coloured, it would be indeed reaching its goal.
But bringing a context to a group of characters, usually well aligned on rows artificially, like in a museum, and in a frame, is not often practised in France or Belgium as it is in Germany or Italy even, but it would add a plus (and more work, perhaps also talent) to the présentation !!
Thnk you to revive this technique !! it gives good suggestions and wishes to try also !!