Positively love your blocks!! Never would have thought to do trapezoids with EPP. You have done it with phenomenal results.
I would not hesitate to recommend Invisifil. BL is a 60 wt and Invisifil is 100 wt, much finer. It acts like silk. It sinks down into the fabric and blends right in so if you are matching a black fabric to white fabric and piece with invisifil in white, it does not show in the seam line of the black unless you really pull apart on the pieces to expose the stitching. Don't be shocked that the spools of it are so small. They can get a lot of 100 wt on those little spools.