Generally in a case like that you would need to connect the effector to a mograph sample node and then connect that to your property, but I don't think it will work in this particular case because you're trying to change a child of the clone (the spline) rather than the clone itself. Consequently any change will affect all clones equally.
If I understand what you're trying to do, you might be able to use the cloner's blend mode with the plane effector to change both scale and the radius at the same time. The key there is to set the effector falloff to inverse. Example:
3689_blendeffector.c4d.zip