^ Understood, I think I can better visualize it now that I've been able to examine the replacement calipers while they're off the car. But it sounds like even in your case you ended up having to file down the pads somewhat. In my case, I placed my ground-down pads on top of the unaltered pads I received from StopTech and the ground down pads are a good 1.5 mm shorter, so I'd be amazed if burrs on the abutment plates and/or pad backing plates could account for that much of a fitment difference, and I'm pretty sure that burrs that severe would have been noticed by either the installer or myself. I'm also not crazy about hammering down the bump because I assume that's there as an anti-rattle measure to keep the pads quiet on the road, which I'd like since this is my DD.
But the bottom line in my mind is still that if the abutment plates and/or pads need to be deburred to fit correctly, then StopTech should be doing that on their products. As it stands, they sent me new StopTech calipers and new StopTech pads that didn't fit together. Why they couldn't have tested them before sending them out after I precisely described my issue to them I have no idea.
I think at this point I'm just resolved that I'll be grinding down pad backing plates from now on. I'll take a precise measurement of my current modified pads so I know the spec and then bring new pads to a shop and ask them to grind them down to that number. That way I don't have to leave my car with them for test fits every time I get new pads.