I think I know what you're talking about. It is kind of awkwardly worded...but being from Grandt, it isn't awkwardly engineered.
There is a piece which has a couple tabs which stick up and it is slightly wider than the cupola is long. These rest above the roof on the inside of the cupola while the flat side faces inwards.
The ends of the cupola go inside the sides of the cupola. I can upload a picture and post it in a few days.
Michael