  We compute the bare step-scaling function $s_b$ for SU(3) lattice gauge
theory with $N_f = 12$ massless fundamental fermions, using the
non-perturbative Wilson-flow-optimized Monte Carlo Renormalization Group
two-lattice matching technique. We use a short Wilson flow to approach the
renormalized trajectory before beginning RG blocking steps. By optimizing the
length of the Wilson flow, we are able to determine an $s_b$ corresponding to a
unique discrete $\beta$ function, after a few blocking steps. We carry out this
study using new ensembles of 12-flavor gauge configurations generated with
exactly massless fermions, using volumes up to $32^4$. The results are
consistent with the existence of an infrared fixed point (IRFP) for all
investigated lattice volumes and number of blocking steps. We also compare
different renormalization schemes, each of which indicates an IRFP at a
slightly different value of the bare coupling, as expected for an IR-conformal
theory.
