Actually, on this type of plane "down thrust", pointing the prop down in reference to the actual thrust line, will cause the plane to climb even more. It's all about the "angle of attack" (AOA). By pointing the prop down, your increasing the AOA between the prop and the wing the greater the AOA of the wing the greater the climbing. Example: engine on plane is at 0 degrees and the wing has a 2 degree incidence- thus you have a 2 degree AOA for the wing. Now if you add 2 degrees of down thrust plus the 2 degree wing incidence you end up with a 4 degree AOA for the wing- which will cause the plane to climb even more. Think of it like this: the prop is going to pull straight- no matter if you put in down thrust- and if its set at 0 degrees the only AOA will generated by wing incidence. Acyually putting in a little "up" thrust might help reduce the climbing. But, you have a high wing flat bottom airfoil with a relatively large engine up front and I doubt that you'll ever be able to trim out the climbing tendencies associated with the throttle.
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