Max,
I haven't read that you have considered place percent. I am sure you will find this is an excellent starting point. There are many possibilities where you can get winners that others often miss and so the odds are better. This is what overlays really mean in practice.

For example try this:
Ignore 2yo and 3yo races.
Consider races up to 2000m.
Consider all horses with a spell in their last six form figures.
Eliminate any that have won since the recent spell.
Select the horse from those remaining with the highest place percent. (Or the top two if you like to bet two)