  In realistic unified models involving an $SO(10)$-like pattern of Dirac and
heavy right-handed (RH) neutrino masses, the lightest right-handed neutrino
$N_1$ is too light to yield successful thermal leptogenesis, barring highly
fine tuned solutions, while the second heaviest right-handed neutrino $N_2$ is
typically in the correct mass range. We show that flavour coupling effects in
the Boltzmann equations may be crucial to the success of such $N_2$ dominated
leptogenesis, by helping to ensure that the flavour asymmetries produced at the
$N_2$ scale survive $N_1$ washout. To illustrate these effects we focus on
$N_2$ dominated leptogenesis in an existing model, the A to Z of flavour with
Pati-Salam, where the neutrino Dirac mass matrix may be equal to an up-type
quark mass matrix and has a particular constrained structure. The numerical
results, supported by analytical insight, show that in order to achieve
successful $N_2$ leptogenesis, consistent with neutrino phenomenology, requires
a "flavour swap scenario" together with a less hierarchical pattern of RH
neutrino masses than naively expected, at the expense of some mild fine-tuning.
These results may be relevant for other $SO(10)$-like unified models where
$N_2$ leptogenesis is necessary.
