Difficulties related to stray interferometers exist and are important, but are not addressed in our paper, as the referee points out. We are assuming that the effects can be minimized in a fountain geometry using a variety of experimental techniques. In any event, a discussion of these effects is beyond what we are able to discuss in this article.
The fountain is assumed to be exactly symmetric (see line after Equation (100)). It is well known that with symmetric fountains diffraction with retro-reflected laser beams produces stray interferometers... Minor Remarks