Yep 13 wins and it might boil down to how tired GWS are in round 22 when we play them and how focused we are and thus how big our win is. That will determine I think whether we need to just beat Essendon in rd 23, whether we need to win by over a certain margin or whether we are in the eight and possibly a win against Essendon may get us a home final.
As I have mentioned 13 wins will get you into the Top 8 this year.