The specs are based off the simple measurements of our pantry shelving.  As you can see in the photos, the original commercial bracket is made from softer material, which is also smaller and does not possess a lot of rigid strength.

My daughter helped design this off simple specs - 16mm shelfing, with smoothed edges are corners.  We printed this in PETG.

When printing with 6 walls, the infill becomes irrelevant.  Print it in the orientation provided with the strong supports to keep it upright (the outer supports are required to stop the two halves becoming loose before they merge).  The 45 degree cross print should also provide better strength.

Dimensions can be modified to fit any corner shelf size.