This paper contains some ideas and procedures to obtain and use previous knowledge of the laws of the layered structure growth for improving the performance of supermirrors. The parameters for correcting the deficiency of supermirrors should be calibrated for each sputtering machine individually. The interfacial roughness growth in CoFeV/TiZr coatings produced at the sputtering facility DIOGEN (PNPI, Gatchina) was studied. This information was used for designing a polarizing neutron supermirror with a reflectance 0.7 at a critical angle exceeding that of Ni in 2.5 times (m=2.5). The experiments confirm that interfacial roughness and interdiffusion, which reduce the reflectance, may be taken into account at the stage of designing to build supermirrors with a maximum reflectance achievable with given materials at a given sputtering plant.