It occurs to me that a shellworld should suffer from certain technical issues of heat dissipation. In fact, for a level as low as the Ninth to even have seasons at all would require deliberate selective refrigeration. This makes one wonder. The implication of Chapter 22 is that "winter" is caused by light and heat from the Rollstars being partially blocked by ceiling features, but in such an enclosed environment, it seems somewhat improbable that such obstruction alone could cause "seasons" in this way. In an enclosed layer, one would think the problem not so much one of warming the Layer as of dissipating waste heat from it.
(David Morgan-Mar made a good short analysis of the similar thermal problems of Coruscant as a footnote in Irregular Webcomic.)