When sewing slash pockets, it is good practice to overlay each corner stitch with an additional stitch applied at a short stitch setting. This second stitch should be added directly on top of the existing corner stitch at about 1" distance from each corner point as shown above. The stitch overlay should be done prior to cutting the pocket opening.
In the construction process, the pocket opening is cut into each corner, right next to the corner stitch. The reinforced stitching provides more strength and stability at each corner which is the most vulnerable and wear are of a slash pocket application.
The double stitch overlay locks the fabric threads which prevents the edges from unraveling or pulling through to the right side of the pocket application.
You should reinforce slash pocket corners regardless of pocket shape and whether the corners are inward-facing or inward facing as shown in the star pocket example above. The overlay stitch is added at 1" distance from each corner along all existing stitch lines.
In order for the star-shaped pocket to lay completely flat and tension free, you will have to slash into each corner right next to the stitching. The double stitching will provide the much needed strength and stability at each slash corner.
The finished corners should lay flat and tension-free why also maintaining their strength during the pocket's life cycle.