I have personally observed a full moon, at sunrise, where the sun is visible on the eastern horizon, and the moon ~30 degrees above the western (an estimate using they height of my fist at arm's length as ~10 degrees, which I understand is customary among amateur astronomers). RET predicts that a full moon must occur when the angle between the moon and sun in the sky is 180 degrees. I am aware of the alleged atmospheric phenomena that can cause full moon and sun to be visible at the same time, but I do not expect that this would predict the moon appearing 30 degrees above the horizon. There were reasonably tall buildings in that direction; it was above them all.
To this end, I agree that the moon is a source of light in its own right. The nature of this light, and why its cycles seem to follow its position in the sky relative to the sun (but as we see, not always as predicted) I do not know, but I can tell you that based upon this, and several other observations of the moon phases and sun's position not making sense, that it is the situation that makes the most sense to me.