I do think the tall one is the most "stormtroopery". Its the way the idealized trooper would be -- and looks like the badass ones in the movie. But personally -- I think, by pictures -- that the short one reminds me more of the actual troopers, I don't know why. Maybe because he doesn't fit quite right in his suit like so many of them in ANH. Also, if you watch the scene where Vader is observing the M. Falcon, there's a mean little shorty trooper off his left shoulder that I always thought was one of the meanest looking trooper in the entire movie. Shorty reminds me of him. Weird the odd things that stick with you as a kid.
What do you think, I'm thinking I might put a little foam in the shorty's shoulders just to broaden them a wee bit. The only I agree with is that the shorty does seem to have slightly narrow shoulders. I also think you could pull his cod piece down a bit to show more of that stomach armor. Think that would do anything?