Merger rate density of BH-BH mergers for various assumptions about the common envelope and BH natal kicks. The possibility of development and survival of the CE phase with a Hertzsprung gap donor, increases the low-redshift BH-BH merger rate density by ∼1 order of magnitude: compare models M30.A and M30.B (a similar effect is found for other models). Natal kicks tend to decrease the BH-BH merger rate density by ∼1.5 order of magnitude: from fall-back attenuated natal kicks (almost no BH natal kicks: model M30.B) to full scale BH natal kicks (as high as observed for Galactic single pulsars: model M33.B). We note that the degeneracy between the tested input physics; by applying high natal kicks we can bring model M30.A down to agree with the LIGO/Virgo estimate, or by allowing for HG CE we can bring models M35.B and M33.B up to also match the LIGO/Virgo constraint.