Top 6 teams double up against 2 or 3 of the other top 6 teams. From that pool we got Melbourne, Collingwood and GWS. No room for WC. We played them once over there in 2018 so it’s about right that we play them once over here this year.
This has never been the case, because there are some guaranteed double ups no matter what the ladder position is of their respective teams (eg western derby, showdown, NSW/Qld derbies, Essendon v Collingwood etc etc etc).
The grouping of teams of 1-6, 7-12 and 13-18 is simply to ensure teams are more likely to double up with those roughly around the same ladder position.