Bhagwan, a suggestion:

You could scale this to individual races by looking for the runners above the middle rating.

In each race look for the highest rated runner and the lowest rated. Establishg the mean between these two ratings. Selections are then the first four above this mid-point.

Example:

If the top rater in the race = 100 and the lowest rated horse is rated 90, the mid point is 95. So, first four runners rated 95 or above.

Quick and easy to calculate. In effect yopu divide the field in two and seek selections in the top half where the great majority of winners are found.

Hermes