Here is my heirachy of axioms.
Each condition overrides all conditions below it.
1 a The last remaining player wins a prize
b If there are five or more players, the second last remaining player wins a prize
c If there are seven or more players, the third last remaining plater ins a prize
2 a Prizes of under 1/2 of the buyin are pointless
b Prizes should be in millions of isk
3 a A particular place (first, second, third) should receive a larger prize than they would if there were less people
b Prize winners should not benefit more from the addition of an extra player more than those that placed better
c Extra money in the pot due to more players should be distributed as evenly between prize winners as possible