I cannot find references, but prior to the Pad Abort test, for years, it was stated or implied that the test would take place from a platform at LC-40 that would simulate the height of the first stage for realism.
But looking at pictures SpaceX sent out, of the Pad Abort unit at LC-40, it is clearly at ground level. You can see the nozzles from the Niagara water deluge system right next to it, which are usually seen in images of the engines igniting.
You can see the pipe of the Niagara water deluge system, blocking our view of the engine in this photo to make the point of how close to ground level the Dragon is sitting.
Hans Koenigsmann in the pre-test briefing suggested that there would be a truss structure to attach too, which I interpreted as something larger, and is most likely the upper right part of the image, with the umbilical connectors.
So what changed between the plans for using a platform high up, to a test down low. (A consequence noted in the press conference is that the lightning towers needed to be disassembled or maybe just the wiring removed to avoid a collision).