Try this.
Delete the horses with the highest & lowest wt rating out of your 5 selections. (100pts etc)as per TABQ & back the remaining 3 ,same amt on each.

Target races where the fav is paying $3.30+

You should end up with a strong strike rate.
You are also targeting races with some value ,which is a must if you are going to do multi betting, because its the short paying favs getting up that will kill this plan if you dont.

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Cheers.