Changing the P Frame Spacing, to gradually increase in distance between each other

In an attempt to create this tunnel, I am trying now to change the spacing between the surfaces. I intend on having it so the spacing between the surfaces increases along the form. Here are the attached files. Inside is the baked file and the parametric model. My intention is to change the spacing according to a point attraction.

Help would be great

thank you

Tunnel.gh

tunnel.3dm