On this process, I work from the middle of the piece and away from it a bit at a time. For understanding of the photos, I am using black batting ( dream poly) for this project... and a red/orange batik backing seen at outer edges. To get started, you can see I've laid out an almost checkerboard pattern on a few inches of the batting.
I'll then carefully place the top in place over the fusible web, then press according to instructions in the package.
Now, the sandwich is fused front and back . As part of my normal quilt prep. process I fold and pin to the front the outer edges of the backing area that isn't fused. It only took one failure in the past when not securing the loose edges of a backing to find it's quick insurance to do so to make absolutely certain nothing somehow folds backward into future quilted areas. ;-D