Because of moveout, this is not the case at any other offset. So the question is what velocity to use, and whether, in typical land and marine survey situations, the residual time shifts are greater than a half-wavelength. No equations are needed to answer this question. All that is needed is the general observation that conventional common-midpoint stacking suppresses multiples because they have lower velocities than primaries. To make matters worse, the amplitude relationships that we expect at zero offset are messed up.
Reflection coefficient is a function of angle.
But on a seismogram from some particular offset, each multiple reflection will have reflected at a different angle. Vertical incidence timing relationships are approximately displayed on CDP stacks. The practical difficulty is that the CDP stack does not mimic the vertical-incidence situation well enough to enable satisfactory prediction of multiples from primaries. Before stack, on marine data, moveout could be done with water velocity, but then any peglegs would not fit the normal-incidence timing relationship. Since peglegs are often the worst part of the multiple-reflection problem, moveout should perhaps be done with pegleg velocity.