I'm not an electrical expert, but those figures seem to be normal to me. I've had the "problem" of fluctuating headlight power on my last three cars (Skoda Octavia, VW polo, and now StreetKa). Due to the load on the electrical system, due to a number of factors such as current draw when driving on snow with the front and rear demisters on, windscren wipers, air-con and recirlculation on and a heated seat (on the StretKa), the headlight power rises and falls with the numbers of revs the engine is producing. With the VW-based cars, I would also get a click from a relay as power was transferred from one part of the circuit to another as the revs rose above (or dropped below) a certain point. Then I'd get full power for the headlights.
With the recent snow, the amount of drain on the battery will have been high as I struggled home the eight miles across country at less than 30 mph in as high a gear as possible, whilst trying to keep myself warm by having a lot of electrical gadgets on. With the battery being much less powerful on the SK than the diesel VWs, I may have to consider wiring on a trickle-charger lead, as I used to do on my recently-departed motorbike, to stop the alarm draining the battery.
This is happening with engine ticking over with or without all electrical items on,It does it any engine RPM