creating finite faults

I'm trying to create a finite fault for my geological model, but no matter what I do Leapfrog extends the fault all the way out to my GM boundaries.  I created my fault by drawing a polyline (to the correct length) but then when the GM creates it as a fault plane, it suddenly extends out.  The only YouTube help there is, is an example of a previously created "finite fault" CSV file simply being added to the scene, not actually creating the fault.  How do I make my fault stay the same length as the polyline I draw?