I was noticing on my photos the sides of the newly added kidney shims were 'flaring' out too much, as the bend matched the inner contour of the kidney plate, but did I did not shape it correctly for the bend to match to the abdomen. You can see on these pics how it is bending out away from body rather than matching the abdomen.
So after consulting with FISD search forums, decided to give the boiling water trick a try rather than the dreaded heat gun. The water seemed more forgiving in case I screw up.
I dipped it in the pan while boiling (just the end part of the shim that I wanted bent, not to the part of the actual weld) for about 20 seconds. It took a couple of dips after the initial one to get it to start to move, but then I slowly was able to bend the sides in a bit. You have to be careful not to press too hard near the area of the weld, or this would pry apart!
Pretty happy with the results! I need to tighten my strapping a few mm still, but the bend is much better now between the kidney and abdomen! Sorry about the sorry pics, used the phone and not the good camera.