I was talking about the “groove” stitching goes into.
If you look at this picture carefully, you will see that only central part of the stitch is somewhat above the leather, the rest is “indented” into leather itself. If it is machine stitching, it’s usually caused by machine foot and needle pressure, if it is handsewn, small strip of leather is removed in advance to make stitch “fall in place” better.
It’s a mistake I see a lot of people making, their stitches look like they are just glued on top of leather, which is why I personally have my custom brushes or just do the stitching in Painter.