I see...your traffic is almost entirely dependent on Adwords.
Not at all. Maybe 20-30%, but that's not the point. The point is, once you calculate how much money you're making per click, you need to use that to determine your maximum bid. Do you want your bid at 50% of the value of a click? You don't want it at 0% or 100% because you won't make any money. The questions is, at what point between 0% and 100% is your total profit maximized.