I'm sitting here still thinking about this. . .
It seems that the requirement becomes a volume of space that is covered by the GFI. That is, a sink "GFI zone", for a sink mounted in a 3' high counter, will include an area of the 8' high ceiling above the sink, as well as the clock outlet on the wall above the sink.
And, if the sink is mounted against a "half wall" partition separating a single area into a kitchen and eating area, the receptacles within 6' on the eating area side of the partition should also be GFIed.
