  We present results from a hybrid description of Cu+Cu collisions using 3+1
dimensional hydrodynamics (MUSIC) for the bulk evolution and a Monte-Carlo
simulation (MARTINI) for the evolution of high momentum partons in the
hydrodynamical background. We explore the limits of this description by going
to small system sizes and determine the dependence on different fractions of
wounded nucleon and binary collisions scaling of the initial energy density. We
find that Cu+Cu collisions are well described by the hybrid description at
least up to 20% central collisions.
