As Anne said above this example is not perfect but I think it give an alternative method that might be worth considering. I am working on a scrap and using contrasting color thread so it shows up.

The material and location for the pocket is shown below.

CIMG0005.jpg

Once the location is identified I picked the piece of material I would use for the welt.
CIMG0006.jpg

I then marker off the bottom and sides of the pocket position.