best way to join center rear

[Tarheel]

I looked at your other post (about cold weather and denim kilt). Are these sewing examples for denim? If you use denim, the lap joint works but leaves a bulge where the seam meets and usually the stitching is obvious. I recommend the first example but understand the limitation of your sewing machine.

The last example will be less obvious (but still visible) to the outside of the garment but is not the strongest stitching solution (even if you sew the "flap" to one side of the adjoining fabric.

I hope our members that have more experience will submit comments to lead you better than my simple view.