I'm assuming that you want to award the points every tournament? If so, you want to be on the Game tab, and enter the formula in the points for playing box. I'm sure there's a MUCH easier way to do this than what I'm providing here, but this would work in the interim.
switch(r, 1, 100, 2, 80, 3, 60, 4, 50, 5, 45, 6, 40, 7, 35, 8, 30, 9, 25, 10, 20, 11, 19, 12, 18, 13, 17, 14, 16, 15, 15, 16, 14, 17, 13, 18, 12, 19, 11, 20, 10, 21, 9, 22, 8, 23, 7, 24, 6, 25, 5, 26, 4, 27, 3, 28, 2, 1)
29th and worse gets only one point and since the switch looks at the player's rank (r), it'll assign the points associated with a top 28 finish, otherwise it'll award one point. Hopefully someone can figure out an easier way, but again, this should work for the interim.