As a diorama judge for many years, my first question when I look at a diorama is "What story is it trying to tell me?" Those that make it very obvious, very quickly will have a greater chance of making it to the Final Three for that category. Another criteria is the consistency between items on the diorama. For example, if showing a desert scene, and 5 vehicles have matte finishes, but the 6th is glossy, I go read the entry sheet to see if the builder discusses why he/she did it this way. If there's no explanation, that inconsistency will make further progress more difficult during the rest of the judging session. The use of space is considered, but not as heavily as these two criteria. I hope these comments help you!