LOL...Ken know all too much about these categories!!

I guess to keep it simple:

1 - Diorama -   Figure + scene + story

2 - Diorama -   model + Figure + scene + Story

3 - Vignette -   Model or Figure + Small Scene

4 - vinrama or diorette - Your guess is as good as mine ;D

Still the first three will always give rise to contestation!!