I found some Loomis pages on composition that you might find useful: http://www.fineart.sk/index.php?s=40&cat=13
Using more negative space (80/20) than positive space can show isolation.
–In the desert a low horizon line, lots of empty sky and a lone man seen from a distance makes the man seem alone and insignificant.
A balance between negative and positive space is still a lot of negative space in a picture.
–A character in the foreground with a stormy sky or a sunset in the background gives equal importance to the figure and the sky. The sky has to be beautiful enough or important enough to the piece to vie for attention
–Batman is sitting atop a church steeple high above Gotham. Positive space is Batman, the steeple he’s on and the city below. There’s still lots of negative space (sky) to show how high up he is and there’s the irony that one can find seclusion in the city if you know where to look. 
–A single figure in the center of the picture frame. There’s no question here where the artist wants us to look, is there?
Most scenes use more positive than negative space. The challenge in these pictures is using color, composition, shading, etc to show the viewer what details are most important. Too much to cover there – ask Loomis. 
Hope that helps a bit.