Objects appear larger than they should at high redshifts. This observation is a hard constraint on the mechanism of cosmological redshift, and has been used to demonstrate inconsistency in previous tired-light models.

The following is a rough interactive simulation of the diffraction pattern of two identical sources of light. The redshift factor is the total redshift (z) at the far-right edge of the simulation (assumes linear relationship). You can see that as the redshift increases, the size of the diffraction pattern also increases. Since an image is essentially a complex diffraction pattern focused onto a detector, it stands to reason that an image of a redshifted galaxy would be subject to the same effect, rendering the observed size to be larger than the actual object.