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tokens: as [see equation ( 1 )], but at the same time the additional power would increase AGN feedback, which is proportional to the luminosity. If we instead increase the BH feedback efficiency, i.e. the constant of proportionality with luminosity, the gas surrounding the BH is less cold and dense, causing BH accretion to decrease. To quantify these effects on the dual-activity observability time-scales, we compare Runs 02, C3 and C4, which differ only by the initial BH mass or feedback efficiency. Increasing the BH mass (by a factor of 2.5) increases the dual-activity time, but only by a factor ≲2. Increasing the BH feedback efficiency (by a factor of 5) tends to decrease the normalized dual-activity time, although the factor widely depends on the filter one chooses (see Fig. B8 for more details). We note that different prescriptions for BH accretion (e.g. taking into account the angular momentum of the accreting gas; Debuhr et al. 2010 ; Hopkins Quataert 2011 ; Anglés-Alcázar, Özel Davé 2013 ; Anglés-Alcázar et al. 2015 , 2017 ) or AGN feedback (e.g. Newton Kay 2013 ; Wurster Thacker 2013 ) may also affect the results. 4.4 Comparison with other work In this section, we compare our dual-activity time-scales to a few select studies, both observational and theoretical, to validate our results. 4.4.1 Comparison with observations Most surveys provide the total number of AGN pairs out of the total number of AGN (e.g. Shen et al. 2011 ). These results are difficult to compare to ours since, by construction, we do not simulate isolated galaxies that could be harbouring a single AGN. Koss et al. ( 2012 ) study the fraction of dual AGN in the all-sky Swift Burst Alert Telescope (BAT) survey. For each of the 167 BAT AGN from the survey, they search for apparent companions, finding that 77 of them have at least a companion 8 within 1–100 kpc. Of these 77 companions, 15 have an AGN, making the fraction of dual AGN systems out of interacting systems (in which at least one system has an AGN) equal to 19.5 per cent (15/77). If we divide their sample in major and minor pairs (defined as pairs with mass ratios > and ≤0.25, respectively), the fraction changes to 37.1 per cent (13/35) for the major pairs and to 4.8 per cent (2/42) for the minor pairs. Since in this case only interacting systems are considered, we can compare the numbers from Koss et al. ( 2012 ) to our results. To do that, we simply consider, for each of our mergers, the dual-activity time when the BHs are at r > 1 kpc (our galaxies, by construction, are never above r ∼ 90 kpc) and divide it by the activity time at the same projected separations. 9 In Fig. 7 , we show the normalized dual-activity time above 1 kpc, 10 kpc and 150 km s −1 , for all our simulated mergers. We also show the results of Koss et al. ( 2012 ) for their full sample of BAT AGN and their subsamples of major and minor pairs. If we neglect the 1:2 merger with high BH feedback efficiency (Run C3), which obviously has a much lower