So, the sun is always in sky. The sun is actually much smaller than RET theory suggests. What is happening at a sunset then? If the sun was always in the sky, when it gets darker, it would dwindle in size until there was no more light. However, when I observe a sunset, the sun's size is constant, and it appears to sink beneath the horizon. Now, if the Earth were semi-spherical, or if the sun revolved around our flat Earth, that would explain this effect. However, you can observe any sunset and see that the sun exits the sky, while maintaining its size. The theory you suggest is observably wrong, and the test can be repeated every night.