Sources with orbit period modulation III: stacking significant modulation: for the small seed (SE) model, the cumulative number of sources at any instant which could be recovered by a survey with 1 day ⁻¹ (thick) or 7 year ⁻¹ (dotted), assuming 1 year observing time and stacking all N _obs flux measurements into a composite statistic. Each curve is directly comparable to the dark blue curve in Figure 5, after shifting the flux scale of the latter by .