I’m asked this question often. While the X-Head covers the central area of the cam
cover, the whole top is open and the shape has openings at the front and back of the part that is open to the air. That is not as important as the fact that these “oil head” engines are both air and oil cooled and are thermodynamically robust. The highest temperature concentration is around the exhaust port where it can go to over 330 degrees F at idle, but the finned cylinder where combustion occurs is totally exposed to cooling air all around. Temperatures at the cam cover, where the cylinder guard is mounted, can range around 180F to 225F. It encloses the cam/valve train which is cooled by oil that is constantly circulated by the oil cooler up front. The addition of a guard over a relatively cooler extremity is benign in the bigger scheme of how the engine handles heat.
On my own 2010 R1200GS with X-Head cylinder guards, whether I am riding the highway or going at a snail’s pace over a trail even during this summer’s 100 degree heat, the temperature gauge always remains at 4 bars, the middle position. BMW’s own aluminum cylinder guards cover almost the same area which verifies that a cover causes no ill effects. Considering the design of your RT, however, the X-Heads look the best while being functionally effective.