Nearfield Measurements of an Antnna on a Cylindrical Surface

Hi everyone

In Cylindrical Near-field Measurements, is it neccesary for the cylindrical surface on which the measurements are to be taken to be centered on the phase center of the antenna under test?

The paper ive mainly been using is "Probe compensated near-field measurements on a cylinder" by W. Leach and D Paris. Does the equations in that paper account for a measurement surface that is not centered around the phase center? I've made a couple of simplifications to the equations (i.e assuming probe is ideal etc)and it seems like my resulting spectrum does vary when i shift the center of the measuring surface.

thanks