Network surface problem for triangulation

I amn trying to create a cupola and triangulate it in equal triangles  in grasshopper  but when i try to create the surface with network surface the guidelines of the surface start all of them from the corner instead of being paralels (as you can see in the image). In that way i dont know how to create the triagles with more or less the same size, because when the triangles go closer to the corner they are deformed. How can  i fix it?

(in the las image you can see what i am looking for)

Thank you