Simple rules should be simple to understand the reason why they produce the results they do.

It is well documented that animals starting in that price range are the most favourable betting targets.
The return would be around the Minus 8% or so mark.

Animals at smaller saddlecloth numbers are there usually because they are of better ability.

So if you eliminate races where order is decided by alphabet or sex or age, then I would think your losses will be reduced.