Cathodic protection of pipelines: is the standard potential too low?

One of the fundamentals of cathodic protection is that a steel structure immersed in an electrolite is protected from corrosion if its potential with reference to a copper cell is −0.85 V or less (in the negative sense). Another fundamental of cathodic protection is that, to obtain correct results, the reference cell should be as close to the cathode as possible. For pipeline corrosion surveys and maintenance this condition means that the cell will be placed over the pipeline, the distance from the cell to the pipeline then depending on the pipe depth. The question is therefore raised: is −0.85 V the correct protection value when the reference cell is on the surface over the pipeline but perhaps 3 ft away from it?