This may explain why the cap stone is missing. The king's star soul represented by the Ben-Ben (Cladking!) is in heaven. The Pyramid on the ground represents the rest of the Osiris-king. Maybe the cap stone was entombed with the king in a chamber beneath the summit?
Robert's brother Jean-Paul has an interesting architectural take on the (symbolically) missing cap stone concept based on the indent of the sides.
Alan Green also has a great theory on the symbolically missing cap-stone he interpreted from Shakespeare's Sonnets, which are all about the Great Pyramid it turns out.Alan Green
I am not sure if Alan has published the cap stone concept though he has given seminars on it. Best thing is to contact him if you're interested. I don't want to spill his beans.