No - I wasn't having an issue with the sew & flip corners and points were matching up just fine. The FW was stitching up a storm, just as smooth as can be. I like these units! I am much further along than this picture shows but not quite done...yet.
My concern was the ongoing quest to find a good marking tool for drawing the guidelines. I need the lines. I'm not going to even try to eyeball the stitching on a diagonal. On black fabric, it's hard to see most everything I tried. Until now.
I had started with a standard silver quilt marking pencil. And quickly got frustrated. The pencil needs to be sharpened every few lines as the fabric smooths the lead out too much. The lines were faint and they rub off too quickly. But then I remembered - Gelly Pens. I bought both a silver metallic and a white one at Michael's ($1.99 each).
Given my black batik has a white/grey/cream flower line design on it, I decided the silver would be the one to use.
Check out the difference between the silver pencil on the left and the Gelly Pen on the right. SO. MUCH.EASIER. There are a LOT of end squares in Clue #2 of the Grand Illusion mystery and sewing them up is much quicker with good lines. It's all about having the right tool for the job.