007Ian,
I am running into a similar problem because I have a similar setup as far as point payout. We have significantly smaller fields, but I do adjust how many are in the money based on number of players and those who finish in the money get the added bonus of more points for the same reason -- the last place money finisher only gets his/her money back. In addition, any player that plays gets at least one point, making it detrimental to miss one of the tourneys in the season, and also giving the winner more points based on how many people actually played. Here are the formulas I use (courtesy of Corey) to take a look at to maybe get some ideas??
For paying 5:
=IF(r=1,(n-r)+7,IF(r=2,(n-r)+5,IF(r=3,(n-r)+4,IF(r=4,(n-r)+3,IF(r=5,(n-r)+2,(n-r)+1)))))
For paying four:
=IF(r=1,(n-r)+6,IF(r=2,(n-r)+4,IF(r=3,(n-r)+3,IF(r=4,(n-r)+2,(n-r)+1)))))
For just paying three:
=IF(r=1,(n-r)+5,IF(r=2,(n-r)+3,IF(r=3,(n-r)+2,(n-r)+1)))))