Its excellent that you have delved into your past figures and are trying to make sense of them.
But this is where you are falling down.
Its your paradigm that is mistaken, not your Ratings.
It has been shown many times that if you backed every single horse that runs, you will lose around 15 % of your investment.
This is not some remarkable figure.
It is not just how it is.
It is the exact same figure that is the deduction that those who run the pools deduct.

Usually if you back those that are under , say $10, the actual loss will be closer to 10%, and if over the $10, then your losses will be closer to 20%.
The reason for that is because those under $10 are actually starting at a price that is pretty much their actual Chance of winning.
Those over $10 , actually have a much less chance of winning than their Markey Price would indicate.

This percentage loss will occur whether you only back the topweights, or if you only back Barrier 1, or if you only back the Favourite.
OR IF YOU ONLY BACK THE TOP RATER.

UNLESS.

The TOP Rater is the top Rater because it really is.
After the race, the Winner should have been the top Rater, because it won.
If it wasn't, then the Race wasn't analysed correctly, and the method used to Rate the horses needs improvement.