What is the workaround?
Set it to 2 participants. It'll make it a 1v1 room but only you (the host) and the first person who joins can play in it. However, as I explained, after a match is finished you get kicked back to the tourney's menu and have to press start again to do another match with the same player. If you want to play someone new, you have to delete the tourney and then create a new one with the same rules and everything.