Excellent walkthrough, OP! Your pictures are down, but it's easy enough to figure out what to do with the information you gave.
I'm considering modding my Kraken case, but I'm not too sure how well it'll work with the thickness of the outer case. After all, induction becomes horribly inefficient after one wavelength, and magnetism will obviously be affected. I'm not sure what frequency Powermat uses for their chargers, but let's hope it's longer than ~2 mm. Wish me luck!
I'll report back with results when I attempt the mod. I expect Otterboxes to be roughly the same in terms of efficacy, as well as any ballistic case I've ever seen, so this should apply to those to at least some extent.
ps: if you don't like powermats, I have a feeling this thread may not be for you.