Squared visibility and differential phases for the Be star reference model (Sect. 2) at radial velocities of vel. = −126 km s^-1 and vel. = −200 km s^-1 as a function of ν_obs, the ratio between the length of the baseline, and the distance of the target. The linear correspondence of the phase with the increasing spatial resolution (ν_obs ≲ 1.5 m pc^-1) characterizes the astrometric regime.