I love using applique block designs as features in the quilting designs. The back of the quilt would look as though there is a lot more applique than there is on the top. If the background area needs more quilting I would use cross hatching or any of the other boring fillers.
The seam lines are shown above so that you can see the pieced block I have used as a quilt setting.
In Electric Quilt any block using just squares and rectangles can be used as a quilt setting without doing the maths to make each piece big enough to call a block in it’s own right.
I have drawn a lot of blocks which don’t really appeal to me as blocks just so I can use them as a quilt setting.