Based on your stats, I think it may be helpful to go back to this point then, as you say...

There still needs more to narrow it down... you are going to have to sort the horses most likely to succeed away from the field mostly likely to fail

Let's assume this step can be done on a consistent basis and with a reasonable degree of success, at least for a subset of race types, venues, field sizes etc etc

Then all that remains would be to achieve overs then, and this could be as simple as...
1. taking the bookies openers for starters (best/simplest 'ratings' and free)
2. adjusting for the % book bias = minimum acceptable price($Pm) - any suggestions for this percentage?
3. setting up a SP Bet via BF whereby SP > $Pm

LG

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The trick isn't finding profitable angles, it's finding ones you will bet through the ups and downs - UB