  Many theoretical models of Active Galactic Nuclei (AGN) predict that the
X-ray corona, lying above the black hole, constitutes the base of the X-ray
jet. Thus, by studying the exact geometry of the close black hole environment,
we can pinpoint the launching site of the jet. Detection of negative X-ray
reverberation time delays (i.e. soft band X-ray variations lagging behind the
corresponding hard band X-ray variations) can yield significant information
about the geometrical properties of the AGN, such as the location of the X-ray
source, as well as the physical properties of the the black hole, such as its
mass and spin. In the frame-work of the lamp-post geometry, I present the first
systematic X-ray time-lag modelling results of an ensemble of 12 AGN, using a
fully general relativistic (GR) ray tracing approach for the estimation of the
systems' response functions. By combing these state-of-the art GR response
models with statistically innovative fitting routines, I derive the geometrical
layout of the close BH environment for each source, unveiling the position of
the AGN jet-base.
