The top four and five to eight players cross each other or continue to rank in a single cycle (see if you want to play more games, and the number of cross games is less than that in a single cycle). The last player in each group plays a game to decide the ownership of 17 and 18.
In this case, the top eight players need to play a single round, with eight games crossing (8 into 4) 1 field (4 into 2) 1 field (final or third or fourth place) 1 field * * * 1 field, and 9 to 16.
If you don't go through the single loop, it is 8 games followed by 7 games *** 15.
The last two digits * * * are single loop 8 games+last 9 games.
Maybe so many games. Maybe.