  We study 3-jet event topologies in proton-proton collisions at a
centre-of-mass energy of $\sqrt{s} = 13 {\rm\ TeV}$ in a configuration, where
one jet is present in the central pseudorapidity region ($|\eta| < 2.0$) while
two other jets are in a more forward (same hemisphere) area ($|\eta| > 2.0$).
We compare various parton level predictions using: collinear factorisation,
$\KT{}$-factorisation with fully off-shell matrix elements and the hybrid
framework. We study the influence of different parton distribution functions,
initial state radiation, final state radiation, and hadronisation. We focus on
differential cross sections as a function of azimuthal angle difference between
the leading dijet system and the third jet, which is found to have excellent
sensitivity to the physical effects under study.
