  The co-evolution between central supermassive black holes (BH), their host
galaxies, and dark matter halos is still a matter of intense debate. Present
theoretical models suffer from large uncertainties and degeneracies, for
example, between the fraction of accreting sources and their characteristic
accretion rate. In recent work we showed that Active Galactic Nuclei (AGN)
clustering represents a powerful tool to break degeneracies when analysed in
terms of mean BH mass, and that AGN bias at fixed stellar mass is largely
independent of most of the input parameters, such as the AGN duty cycle and the
mean scaling between BH mass and host galaxy stellar mass. In this paper we
take advantage of our improved semi-empirical methodology and recent clustering
data derived from large AGN samples at $z \sim 1.2$, demonstrate that the AGN
bias as a function of host galaxy stellar mass is a crucial diagnostic of the
BH--galaxy connection, and is highly dependent on the scatter around the BH
mass--galaxy mass scaling relation and on the relative fraction of satellite
and central active BHs. Current data at $z \sim 1.2$ favour relatively high
values of AGN in satellites, pointing to a major role of disc instabilities in
triggering AGN, unless a high minimum host halo mass is assumed. The data are
not decisive on the magnitude/covariance of the BH-galaxy scatter at $z \sim
1.2$ and intermediate host masses $M_\mathrm{star} \lesssim 10^{11}
\,\mathrm{M}_\odot$. However, future surveys like Euclid/LSST will be pivotal
in shedding light on the BH--galaxy co-evolution.
