Maverick, they way I see it is that you are trying to "cross" two seperate methods.i.e.
(1) Betting ratings to prices, say using proven ratings either your own or someone elses coverted to prices, so you ONLY back the overs, the theory is OVER TIME you have to be in front, as you've only accepted a greater price than the horses true chance of winning.

(2) Dutch betting as you say is combining 2 or more selections to win or "take out" a certain amount, now as I've said to Dark b4, if you have say 4 selections to Dutch and you are only going to DUTCH the ones where you get overs/// HUH? it's back to the crystal ball, as how would you know what to bet and how much until AFTER the race?

Just my thoughts.