Hi when you first structure your Variable point scores, you need to make sure you standardise the scores so that when you combine them they have the same impact from Variable to variable ie. that is if you use an Indexing score of 100 then each point should equate to 1 % point if you havn't thought of doing that, then your whole point scoreing method is skewed.
The other method if using only one Variable is by using the Mean & Standard deviation of each horses life to date history and then finding the Winners Mean score for todays Grade. if you look up Zscore tables on the net you will get a good idea to accuratly assess the Payoff for anything.
The idea is to find the performance envolope of each horse,if you think you find one score or total then thats wrong, look at how standard deviation works and you will get an idea on how a horses form bounces along..