You can control the number of players to start but the minimums for ranked servers are as follows:
32 or less slots - 6 players to start
33 - 48 slots - 8 players to start
49 - 64 slots - 10 players to start
This is the reason that we keep Server 1 at 32 slots, it's much easier to get it running. I'd like to see more players in there too but the server wouldn't run as frequently.
Watson