I think the average number of people who join the queue should be checked, then the amount of time the queue is open should be adjusted accordingly. If all 3000 players are able to join the queue in 30sec, and the warper only accepts 30 players, theres only a 1% chance of being selected. If the join time were cut to 15-20seconds, fewer people will be able to join, giving better chances of being selected. (as I type this, for some reason i think of the Hunger Games)
Not sure if this was thought of: People who are inside towers, spar rooms, or other places where event warps are prevented, should be excluded from the queue to prevent wasted space. (Unless its possible to warp into an event while inside a tower/spar?)