This scale is projected onto a large angle in the anisotropy spectrum both because of the intrinsically large size of the horizon at such late epochs and because the point of origin of the effect is much closer than the last scattering surface. For a fixed matter density, matter domination ends sooner in an open than a lambda universe. Thus the angular scale of the cancellation cut off in the spectrum is larger in a lambda universe. Once fluctuations leave the linear regime, their subsequent evolution can also make the potentials vary with time. In hierarchical models, where the smallest scales go non-linear first, the effect peaks toward small scales.
Gravitational waves introduce tensor fluctuations in the metric.
As we have seen, distortions in the spatial metric can produce gravitational redshift effects on the photons. The difference here is that they leave behind a quadrupole signature. As with the other ISW effects only scales above the horizon at last scattering contribute.