FWIW, aside from the seasons with two divisions, the NBL has used the following playoff formats:
1979: Top 2, both into GF
1980-1982, 2010-present: Top 4, semis & GF
1985-1991, 1998, 2000, and 2009: Top 6, elimination finals for 3-6, 1+2 get a rest
1992-1996: Top 8 with quarter finals, semis, GF
1999, and 2001-2003: Top 6, 1-6 play qualifying finals with winners and highest placed loser going through to semi-finals ('lucky loser' format)
2004-2008: Top 8 with 2 rounds of semi-finals' qualifiers for 3-8 (1+2 rest), then semis & GF
Since its inception, three teams have won the championship from lower than 3rd:
1988 Cannons - finished 4th with a 16W-8L
1990 Wildcats - 5th with 17W-9L
2001: Hawks - 4th with 21W-7L
If you want a mediocre start to the playoffs involving teams with losing records, then top 6 in the current NBL will give you that. Will the fans of 3rd placed team pay to go watch their team beat the scrubbers in 6th?