Matt I had that same problem, drilled all my spot welds, and found out I had 3 not perfectly round spot welds that were still attached to the car. I just used a screwdriver to try and "pry" the plate away from the car and see where the metal seperated and where it was still stuck. I wont lie though, I got fed up with one of them and went nuts with the air chisel, 50/50 regret that haha. Good to see your getting under the plate (only took my 30min to get it off btw )