A competing effect, which turns out to be negligible on small scales compared to density fluctuations but probably dominant on larger scales, is the Sachs-Wolfe effect , basically the gravitational redshift on photons escaping from denser regions. The fluctuation amplitudes are always very small, so that linear perturbation theory can be used. The location of this peak is sensitive to both W and L , while its amplitude is sensitive almost purely to W . Models also predict that harmonics of this peak should be seen to higher values of l . This will modify the spectrum slightly with respect to a perfect single-temperature blackbody, and will be manifested by damping out irregularities due to structure which is smaller than the comoving depth of this apparent shell.
Further details exist, but at about the level of uncertainty in some of the relevant reaction rates.