Sorry to dig up an old thread.
I hit this issue myself and fried some Niles emitters.
I wanted to thank those who posted here.
I also wanted to contribute and share an image I made that illustrates the issue.
The Niles emitter is slightly longer and therefore would hit the 12v connection.
A regular stereo cable I had does not go as deep due to an extra metal 'step' at the base. This makes me suspect a regular stereo extension cable could potentially be used instead of the RTI 'pigtail', however I am going to use the 'pigtails' (better to be safe than sorry).