Mograph clones between 2 splines

I have two splines.  The top spline is linear.  The bottom is bezier.  A small cube is cloned along the bottom spline.  
I want the clones to scale to top linear spline.  how can I accomplish this ?  here is image

One way would be to scale using a plain effector on the cloner with a source falloff.  The source would be the top linear spline.  

I found a solution, but it's a bit of a workaround.
I am cloning Vertical Splines using Object Mode and the Bottom Spline.
Then I'm using a Rail (Top Spline) with Scale activated in the Clone.
That produces the lines with the required Scaling to fit between the Top and Bottom Splines.
I am then using the Sweep to Create the "Cubes" from the Cloned Splines.
..
https://www.dropbox.com/s/jcyq82jz0...001A.c4d? dl=0