Photo by Scott Russell of Sandy Hook, CT.
It is similar to the RS-11 (it uses the same chassis). Atlas twists the truck wires above the end of the board and next to the plug. The wires need to be moved out of the way temporarily so the decoder fits flat. Then the wires can be twisted back out of the way.
Note the DP5X is shown below, but that decoder has since been replaced by the DP2X.