Twisting Ribbons... Help please!

Hello everyone,,

I have been struggling with this definition for a while since I'm new to grassshopper.

What i want to do is have my vertical ribbons start along the plane then have a sudden twist and become rotated at an angle to the plane then twist again to become along the plane's surface. i think i need to control the intensity of the twist in the middle and on the edges. (sharp, gradual, sharp)  

however, i am only able to achieve the twisting in the middle. i cannot seem to keep the ribbons starting and ending with the same line. 

i have attached my definition and an image of what i want to achieve.

Would really appreciate someone's help,

thank you in advance,

Kristy