I’ve found that ~25% of the overall field is the right amount for the queue for a short-but-not-too-short wait between matches for the queued players.
IMO, having everyone in the queue move when the next person enters is overly complicated. Here’s what I do:
- Add chairs for the queue area roughly in a circle.
- Give a “totem” (usually a sweet wooden Pinball Co-op sign, but it just needs to be obvious and not too hard to hold) to the first person in line.
- When Player X joins the queue, they identify Person Y via the totem and tell him/her which machine to join; then Player X sits it in the last position, wherever that is at the time; then Player Y hands the totem to Player Z (the next player in line) and Player Y joins the required game.
This last step seems complicated, but it all happens in about 5 seconds.