  While Fabry-P\'erot resonances and Moir\'e superlattices are intensively
studied in graphene on hexagonal boron nitride (hBN), the two effects have not
been discussed in their coexistence. Here we investigate the FP oscillations in
a ballistic pnp-junctions in the presence and absence of a Moir\'e
superlattice. First, we address the effect of the smoothness of the confining
potential on the visibility of the FP resonances and carefully map the
evolution of the FP cavity size as a function of densities in and outside the
cavity in the absence of a superlattice, when the cavity is bound by regular
pn-junctions. Using a sample with a Moir\'e superlattice, we next show that a
FP cavity can also be formed by interfaces that mimic a pn-junction, but are
defined through a satellite Dirac point due to the superlattice. We carefully
analyse the FP resonances, which can provide insight into the
band-reconstruction due to the superlattice.
