My understanding of the data is that there is a platform on which the pyramid stands, and this platform is about a cubit and a half above the surrounding ground inside the enclosure wall. The casing stones extend below the level of the platform so that the base of the pyramid, as defined from the bottom of the casing stones, is 362 cubits, but taken at the level of the platform it is 360 cubits. It is this number which is taken as the basis of RMP problem 56. (Legon gives an explanation of the distance of 362 cubits as making a distance of 99 cubits to the enclosure wall.)
This platform is also used for the core pyramid which has a base of 300 cubits according to Rossi.
In an article in
DE, Gyula Priskin gives a calendrical explanation for the choice of both 300 and 360. In another
DE article, Priskin also gives a calendrical explanation for the 3:4:5 triangle inside the KC of Khufu's pyramid.
Here's an interesting observation. If you take a pyramid with a base of 300 cubits (the same as the core pyramid, or Phase I of the Bent Pyramid) and a height of 200 cubits (the overall height, or Phase III of the Bent Pyramid), you get a pyramid with a slope of 4:3, i.e., based on a 3:4:5 triangle. Such a pyramid will have dimensions exactly twice those of the sixth dynasty pyramids.