Japanese Fighter Pilot

Why not 1:16? Tamiya has one, this one:

http://www.falconbbs.com/m37-169.jpg

http://www.falconbbs.com/m37-170.jpg

That's a big jump from 1/24. I think it will look too big.

Model maniac's idea will work if you force the perspective, that is show the vignette with the pilot in front of the plane standing in front of a plaque describing the aircraft. This way viewers will know your intent as the 'front' will be obviously the plaque. The same can be done in reverse with the pilot behind the plane in a smaller scale, say 1/32.

That being said I have wanted to do a forced perspective diorama in three or more scales.

SuppressionFire

Model maniac's idea will work if you force the perspective, that is show the vignette with the pilot in front of the plane standing in front of a plaque describing the aircraft. This way viewers will know your intent as the 'front' will be obviously the plaque. The same can be done in reverse with the pilot behind the plane in a smaller scale, say 1/32.

That being said I have wanted to do a forced perspective diorama in three or more scales.

I remember reading something about this technique, which shows depth in a diorama setting. I'll check it it.

Yes it is mainly used in shadow box dioramas. I feel it is to effective of a technique to be used in just one type of diorama. A example would be:

1/16 scale machine gunners in a trench, possible one with a anti-tank weapon. Advancing their position would be a 1/35 scale tank, a few 1/35 scale soldiers with the tank. Behind that 1/48 scale 1/2 track, a few soldiers in that scale as well. In the distance some 1/72 infantry and possibly a 1/72 aircraft in a ground attack roll..

This could happen in less space than you think. Each scale would have a different horizon or hill line. The smaller scales would be purpose built with more blue color for perspective. The viewer is forced to look at eye level with the 1/16 scale machine gun crew. The entire scene is open to get closer looks at the details and individual builds.