It's mounted on the nsf inner wing with a short link rod going down to the lower arm. The wife's had non xenon arms fitted just before we bought it so the front sensor wasn't attached to anything and the headlights were randomly up or down. I bought a kit off ebay, search: FIAT 500 GIULIETTA YPSILON HEADLIGHT ADJUSTER MOTOR HEIGHT RANGE ACTUATOR
After I'd fitted it the lights were still high and I read a thread on here somewhere that mentioned speed bumps fully loaded bending the bracket that the rear sensor attaches to upwards so the system assumes that the rear is higher than it actually is and points the headlights up. I 'calibrated' the self level by parking on flat ground with the lights on a flat wall, laid on the floor at the rear of the car and reached under to the sensor and bent it back downwards until the lights were at the right level. The system only compares the values between the front and rear sensors and adjusts the headlights to suit so lowering shouldn't effect it unless the arms on the sensors are physically running out of travel. If they are the rear would probably be sorted by bending the bracket up and the front by either shortening the link or remounting the sensor slightly higher.
Hth