The chat's sidebar shows, between other informations, a list of avatars of the people currently in the room, ordered by recency of speaking.
This list consists of several rows with space for a number of icons each (which is dependent on screen width). In chatrooms with lots of people in them, this list is clipped at 32 icons ..., which is three full rows and then two more icons at a full screen window here. Then there is the link show 3 more (number varies) which will show the avatars of all of the members.
While 32 is a nice power of two, I think a multiple of the number of icons which fit in a row would be a quite better default number, since then we would have a full rows, instead of the last row having only two icons (which then by clicking the link changes to five icons).
I think three rows could be a quite good first approximation (at least, on my screen).
(Edited after seeing it depends on screen/window width.)