You don't specify if your midarm is a sitdown model or mounted on a frame. Both ways it is darn near impossible to line up the top with the bottom. Some have done it but I will not attempt it. I have quilted two double sided T-shirt quilts on my longarm on the frame and in both cases I quilted an E2E design and did not make any effort to not quilt through the Tshirt imprints. I will only work with silkscreen imprints. I weed out any T-shirts that have the iron on type rubbery ones.
Here are links to the two I have done
http://www.quiltingboard.com/picture...ts-t95274.html
http://www.quiltingboard.com/picture...t-t209647.html