After about 45 minutes of cutting, fitting, trimming, refitting, bending, etc, I end up with a piece that I think fits in the hole with about a millimeter of gap all around.
After that the patch gets sprayed and wiped clean, then hit with two coats of self etching, weld through primer.
And then it gets tacked into place, tapped with a hammer until it fits, then stitch welded all around. Once I'm happy I grind back the welds to make sure they are continuous, weld in any areas that need work and grind gain.
This is the final product.
I will note that I ground these welds flush as I could as I know this patch will be visible from the outside of the car even with the trim pieces and inner fender lining on. Paint only does so much and I don't want to have to do any filler at this point in the project.