Goni, It looks to me like the instructions call for the leading edge to be installed with its top surface approximately 1/16" to 1/8" (about 2mm) above the upper edge of the ribs. The pencil line allows you to keep it even. There will probably be some sheeting that butts to this raised section of leading edge. Minnflyer posted while I was typingsame idea, his drawing ins much more helpful.