Made the discovery this week in aspen that certain types of galaxies are actually anti-correlated with MaxBCG clusters on certain scales. These are very luminous galaxies, and the cross-correlations are negative near the virial radius. Considering that more luminous galaxies tend to me more strongly clustered this was a bit of a surprise.
My guess is that this is due to the cluster finder. The cluster finder looks for groups of luminous red galaxies, ranks them by likelihood, and "percolates", meaning that smaller clusters are not allowed to live within r200 of larger clusters. Then if you choose a certain ngals200 this might cause a feature near r200 in the luminous galaxies. I'm checking simulations. I see that the feature is there for MaxBCG run on the sim, although the effect is weaker. Now I'm going to run on the halos and see if the feature persists.