I cut both pieces together with my rulers butted up in a straight across the entire seam I plan to sew. I pin the join together with a very small overlap (just enough to pin) with the points of the pins facing toward the needle and the smaller width of batting on the right. I butt the edges together as I sew with a three stitch zigzag (5 width stitch). As long as the cut is perfectly straight and both pieces can move together, there is NO bunching or puckering. It lays perfectly flat and the join is undetectable to the touch.