My plates worked well for aligning my car after I followed Rob's advice and cut out the central pivot point. I jacked the car up off the plates to make my control arm adjustments. I then positioned the top plate about an inch inward from the lower plate. This allowed the plates to slide outward when the jack was lowered. After experimenting with the amount of outward slide, I was able to position the plates consistently. My degree marks worked well even if the top plate wasn't perfectly aligned with the lower plate. All I had to do was make sure that the top plate was parallel to the 15* marks that I made.
Many thanks to Rob for taking time to help me sort out my alignment issues.
