Projecting evaluated curve Point perpendicular to parallel curve with number slider.

I am trying to make a component where I will be able to control every single point to achieve the desired surface. 

At some point, i am stuck at where I am able to control 1 point along the direction of Evaluated curve & Z direction, but I want that same point to be moved towards the parallel curve (Which I am not able to).

Also, I want to control that point with number slider so that the point should not directly project to that curve but should be able to move in the direction of the parallel curve.