genetics do matter.. as far as what you can control you maximize lights relative to area and hours of use and keep the plant happy while filling the space well.
400g is very easy to get out of a 4x4. even with ambient co2, you should be able to push 50g/sq ft. you can go 20-30% higher with co2 bumped to 1200-1300 ppm.
some plants are more productive than others, so even if you apply the most light possible relative to environment and fill the space well, you will have a range of possible yields. Maybe, not all strains can hit 50g/sq ft but most should.
the more even and organized your canopy is, the better the yield can be relative to genetics.
40 DLI is a good target for ambient co2 and 50-60dli is a good target for added co2.