I think sometimes you need to be careful especially with bets that size.

You have a run of between 10 to 20 and your down a lot of money. Racing involves a lot of luck. You can have a system that gives you the horse that has the greatest fitness, the greatest speed etc... but the best horses lose all the time.

I'm testing a system at the moment with 200 selections for the win and down by 8 units on unitab.

However, there was two horses paying $22 and $41 that went down in a photo.
Give me one of those wins and you have a good profit. You just don't know if you have a winning or losing system.

Good luck