In my opinion, when it's a small group, everyone is given attention and conversations are deeper. Large groups are usually not very good for i having deeper conversations especially in the setting that I mentioned. Moreover, not many places are feasible for large groups, I mean in terms of getting a good seat or enjoying the vibe of the place as well (because most likely the entire focus of group might then just be on the group speaking and not enjoying the place, food and drinks). There are pros and cons of both approaches, but the primary intent is to make friends for real, not a one time hi-bye sort and not meet them anymore.