(Note that I know that dx, dy and dz are DIFFERENCES in x, y and z)
Selecting a box area using dx, dy and dz doesn't work.
it will not work at all.
confirms that it is a bug with dx,dy,dz, because getting in a 3 block range of 100,55,100 will trigger the command!
more details and "proof": https://www.youtube.com/watch?v=7vsmoJ0xXbQ