Economies of scale

I've come to a tricky place in a new piece. I've been composing it without much in the way of pre-compositional planning and it's still unclear whether it'll be eight or 28 minutes long, or whether it'll be for a smaller or larger ensemble. My sense of the potential economics of a piece of music based upon the materials assembled so far is that the longer the piece, and the larger the ensemble, the less material and the courser or broader the contrast levels should be. As it now stands, I have about 7 minutes of fairly dense music in short score, which would -- with a few details and some brief connecting passages added -- probably make a decent piece for a small group of instruments. However, the very same material, though strategic repetition and variation and some thinning out or trimming, might just as well turn into something for many instruments with a duration three or four times longer.

This piece is composed "on spec", without a commission, so the precise make-up of the ensemble and the duration have not been set or determined externally. I have the luxury to let the materials themselves speak to me a bit before making these decisions. In other words: I'll have to sleep on it.