The wiggle room is for the empeg-to-connector connection as the empeg moves around in the sled.

You've said that you're not using the ground wire from the connector, so I don't think that will make much difference (other than actually maintaining the connection, hence allowing music out of the empeg and into the rest of your car ).

If you're getting your ground wholey from metal on the empeg touching metal on the sled, the docking connector won't come into it. (As usual, I defer to those with more empeg-specific knowledge.)

-jk