Density of the universe

Were the universe uniformly populated with matter, the density of the
universe* would be constant across all scales; as the mass enclosed in a
sphere of radius r would increase as r^3.

As observed, matter is condensed into stars and stuff and galaxies and
clusters of galaxies. By the time we are getting to clusters and
superclusters of galaxies, I believe we're told that the large scale
structure is more like a foam, with large voids and matter (as galaxies)
forming sheets and nodes between sheets.

If the suggestion is that clusters of galaxies are found as 'sheets' rather
than 'volumes', does this mean that the mass enclosed in a sphere of radius
r increases with an exponent less than 3? , r^2.5 perhaps?

Do we have an 'accepted value' for the exponent over sufficiently large
scales?


*assuming a simplistic 'static' model