Slope defense is effective in real war and IR tank battle. Slope defense like hull defilade was used very effectively by the US tankers in Sicily and Italy against the Germans. The US Army Shermans & GMC Halftracks would rise toward the crest of the reverse slope of a hill and fire on the German tanks below. The would crest the hill just enough to fire the main gun and then reverse. The Germans would try and lay their guns but couldn't track the pop up tanks. If they hit a M4 most rounds would bounce off the hull slope which was exaggerated due to the hill angle. The German tanks were also more vulnerable if hit from the top. The fins on the IR apple duplicate that angle of defense. It is really one true on the back side of the hill but can be used on the front slope of a hill which would be very unrealistic. It is also avoided since you could be "Pinned Down" on the front of a hill. As soon as you try and move off the front you would be very vulnerable. That is why the better battle systems emulate the Tamiya fins. The fins also keep sunlight off the apple can effect IR range/vulnerability.