The design was developed to create a steeper roof pitch on the top of the dome that will shed rain and snow better than the shallow arch on the original dome. The shallow arch is not as critical on the dome as it is on the center arched sections of the XT Extended dome.
The "pyramid cone top" can also offer substructure for support of the dome when a large cupola is added. On the 15 ft dome it is an extreme case. On a larger dome it is a workable option. The Type 2 cupola is shown, made with extended connector hubs. Last three illustrations show tubes added to make tetrahedral pyramids that add support to the cupola. Click on images to go to a larger view.