There are basic mathematical principles involved here.

It doesn't matter what odds your horse is at if you stake to win money. What matters is your strike rate. Odds only come into play when you consider the risk/reward ratio. $10 to win $200 or $100 to win $200. In preserving your bank, you try to lower your risk and increase your reward, but in the final analysis if your average strike rate isn't up to it...you won't win no matter what average price you can get.
When I do my form, I always make my selections without the prepost odds within reach. I am amazed how many horses I rate at say 3/1 start at 10/1 plus. This way odds never sway my judgement.