I know medina has thought about how to do a tournament with 18, that includes all teams. How about this
Make sure the regular season ends on Saturday.
Top 6 teams advance to Chicago/Indy
Then Monday-Wednesday you have two separate 6 team tournaments, hosted by the #7 and #8 teams.
#7 tournament: #7 and #10 gets byes, #11 vs. #18, #14 vs. #15
#8 tournament: #8 and #9 get byes, #12 vs. #17, #13 vs. #16
Then the two winners jump in as the #7 and #8 seeds in the 8 team BTT in Chicago/Indy, starting on Friday