Hi,
Using the Conditional Operator in the Position on Spline - Less than 50% mode should do the trick. Also, you can get the desired value based on the measurement of the following expression within the Arithmetic Operator:
return XSectionLength;
Once divided as needed (in your case by two) it can drive the Right Padding value of a Transform Operator wired to the Right Side Input. Attaching sample scenes. Hope you'll find them useful.
Best regards,