Large-scale structure density vs. optical luminosity regression parameters for the 0.015 < z < 0.06 groups. Here, α stands for intercept, β – for slope and σ – for the intrinsic scatter. The 2D contours show the 90% significance levels. An optical sample without a 3σ cut is marked with solid grey and with the cut with dashed magenta lines. The compact X-ray sample is marked with dash-dotted black and extended with solid blue. The X-ray clusters exhibit a steeper relation and lower scatter.