Keeping your friends in separate compartments is safer, because the two of them might not get on and some of that would land on you. What you give up is the chance that either one finds somebody they would never otherwise have met. Circles mostly grow because somebody was willing to make an introduction that might go flat. The downside is an awkward hour and nothing worse.

Put two people together this month with a reason attached, something they both actually do. Stay for the opening, then stop managing it and let the conversation find its own way.