I agree that horses with no form at the track or distance should not have zero rating. It would be better to use say a 5 point scale and give these horses 3 points and have 4 points for horses that have performed reasonably well and 5 points for those that score extremely at the distance. Give 1 point for a horse that has many failures and 2 points for at least one failure.

I assume you would have had no bets on winners as your prices were above those on offer.