Analysis of mass-luminosity curves for different subsets of binaries (both visual and eclipsing spectroscopic binaries) revealed the deviation in slopes for relatively close binaries (averaged around 3.6*10-4 light years) compare to relatively far spaced binaries (averaged around 5.6*10-3 light years). The slope for close binaries is larger, what means that for the same luminosity of the main sequence stars the determined from Kepler law gravitational mass is smaller (or gravity between stars is stronger). This observation is opposite to the MOND idea (the far the stars the higher shift from 1/r2 law to 1/r law for gravity) – that would be opposite effect. The idea of dark matter seems to be confirmed once more (as if some dark mass is hanging around the star, thus making the mass seemingly larger), but a new concept of some kind of gravity enhancement by the mass itself may also be relevant – the closer the binary the higher local concentration of mass and higher value of G in the gravity law.