Does the radiator have bypass flaps to allow high speed air a route through when it overwhelms the fan? I don't even run a shroud, just a mechanical 17" fan 1/2" off the radiator. Radiator is a Howe Racing 19x27" dual 1.125" core aluminum crossflow generic. The car stays cooler with the air dam since it keeps pressure down under the hood. Your scoop is doing the opposite and offsetting the gains from the dam. Raising the rear of the hood is iffy if it is too close to the high pressure zone at the base of the windshield. Think about the NASCAR guys using the windshield base cowl induction for power gains. Same high pressure as a scoop without the drag.

Heat extractors, louvers, etc. may help tremendously in creating a lower pressure underneath the hood and really improve air flow through the radiator. It worked wonders on my dad's Firebird running 150+ MPH and keeping under 200°.