There isn't really a "wrong" way. Creating a maneuver and tagging it for effect is the essence of Rick Neal's example above. He's simply taken it a step further and codified the effect you should expect based on the number of shifts. But it's still 3 shifts for the 'effect' (a "Knocked Sprawling temporary Aspect") and 2 more for distance. It works well enough.
You can also use a block simply narrated as 'pushing people away'. Or you could use an attack and negotiate consequences related to being pushed away. Either has the virtue of simplicity and still works well.
Finally, you can remember zones are abstract things and not static areas. They're "loosely defined as an area in which two characters are close enough to interact directly". From a mechanical point of view, the push back spell simply needs to initiate creation of a new zone. Possibly one difficult to enter. Similar to a block in many ways except it will require movement to bypass, not simply a successful attack. When creating such a spell I'd use 2 shifts for the zone, 2 shifts for duration, and say 4 for the zone barrier. Narratively, you have strong winds blowing people away from you for the next two exchanges...winds it will require movement (as well as pushing through the winds) to pass.
Don't get stuck on zones as some measurable discrete area.
