The less teams you have in your final series, the greater the number of pointless games towards the end of the season and the bigger the impact on crowds.
I have suggest before that for an 18 comp we could look at -
Week 1:
Teams 1, 2 & 3 from the season get a bye
Teams 4, 5 & 6 get a Home Final
6 v 7 Friday Night
5 v 8 Saturday Night
4 v 9 Sunday Afternoon
Three winners from Week 1 ranked A, B & C
Week 2:
Teams 1, 2 & 3 from season get a home final
Minor premier always has a double chance
3 v A Friday Night
2 v B Saturday Night
1 v C Sunday afternoon
Two bottom ranked losers eliminated
Top 2 (One & Two) ranked winners get Week 3 home finals as a reward
The 3 winners ranked One, Two, Three plus the double chance team in spot Four
Week 3:
Two v Three Friday Night
One v Four Saturday Night
Winners through to Week 4 Grand Final
Every game is a potential elimination game
The minor premiers are automatically guaranteed a double chance, regardless of week 2 result. Their reward for winning in Week 2 is a home final.
Same amount of games as current but 1 less in week 1 and 1 more in week 2 - so that game is 'worth' more
Plus that Week 2 game can be an additional Sunday game which means during the finals, you get a stand alone final on each individual day
Unlike the current system, you can't get a repeat match up until the grand final
In the lead up to finals, under our currently system you usually have 10-11 out of 16 teams fighting to make the cut.
Under this system you'd have about 12-13 out of 18, so although the number of teams that miss out are roughly the same, the % still in contention is slightly larger therefore improve the number of finals-affecting matches during the later regular season rounds.