I have had a similar issue, with circulators/bubblers running on either side of me. One often opens up the ice all the way over to my dock, 150-200 feet away. The same thing happens on the other side, with that circulator around 100 feet away. My own dock is crank-up.
I oversee the operation of another pair of circulators elsewhere. What I have done there is to use frequent ON intervals of short duration. Right now, I set eight intervals of 45 minutes each, and it seems to work well for the time. Later, when the weather moderates, I'll cut back the length of each interval, then reduce the number of intervals, relaxing things during daylight.
What works well clearly is a function of location. One protected from large expanses of ice that can be moved by wind, however slowly, won't need as much circulator ON time as, say, a location facing W or NW into the Broads.
In most locations, I do think that spreading out total ON time over more intervals is more effective that few long intervals. In general, once a circulator has opened up the ice around the outer half of a dock, staying on won't gain much. When a circulator is running, it moves water, giving it momentum. The longer the device is on, the more momentum the surrounding water gains. We're not talking fast flows away from the circulator, but the mass involved is enormous. It does take time for the energy given to all that water to dissipate, regardless of how slowly the water is creeping, and movement will continue long after the circulator turns off.
Having short ON intervals, coming every few hours, limits ice reforming to any thickness that has much strength to it. Sure, a layer of ice may reform during the OFF time, but it is quite fragile and easily melted out by the next ON interval. Here is but one of many references that discuss speed of ice formation vs air temperature:
http://lakeice.squarespace.com/ice-growth/