What is the strike rate of each of you 3 selections and thier average divi.

I have been down this path and you may find backing your top rated runner the best option, if you choose to back more i would just back your top 2 runners the same amount as long as the price is over $2.50 otherwise back just the one runner that race.

I have tried backing 3 selection and find the strike rate drops off a bit, you will get the odd winner with your 3rd and above selections but in the end they will cost you.

Some people will dutch the selection but this also is a bad idea as when you get the good priced winners in you will have smaller amounts on them.

As we always say if no profit at level stakes then it will fail so test each selection at level stakes and do the sums yourself.