KL divergence of fixed cubic, rod, and slab topologies with fundamental domain side compared to a slab of variable fundamental domain size L. The chimney space T2 dates from the 2013 analysis (Planck Collaboration XXVI 2014) and was computed for the best-fit parameters of that release. In all cases the smallest KL divergence, corresponding to the best fit, appears at , indicating that the slab space can be used to detect other topologies. An additional dip at L ≃ 5.5 / (2H₀) may be due to a harmonic effect at half the size of the fundamental domain; it is, however, much smaller than the drop in KL divergence at the size of the fundamental domain.