As a follow up to my original question: This experiment failed! First I did the separate add on with an overlap. It didn't work well after testing, so I removed all the leaders and stitched them together. Remounted and now have them back on the frame with a large practice piece attached. I'm still not happy with it and also discovered that the Start-Right Leaders themselves are crooked. Measuring from one end to the other, they are off nearly 1/2" on the largest leader and 1/4" off on the other two. For well over $100 buying these, I'm very disappointed.
I may end up buying some canvas and starting over completely. What a frustrating ordeal this has been. Sigh. I just want to quilt something and have spent all this time fussing with the leaders. I know if they aren't right, I won't be happy with my quilts once I get going.