> but in any diorama different heights "would not look right".
Why do you say that? Different heights are a fact of life. A famous example: the Beetles in Yellow Submarine (John Lennon was 5'11", Paul McCartney is 5'11", and George Harrison was 5'10.5", all noticeably taller than Ringo Starr at 5'8"); the animators had to account for Ringo's shorter stride.
Then there's the chronological element: the average height of US soldier during World War 2 was 5'6". In the 19th Century, it was 5'7.75". Even "now" (using 2006 statistics) the average height of a Caucasian American male 20-39 is 5'10.5", not 6-even.