  We analyze a description of twisted graphene bilayers, that incorporates
deformation of the layers due to the nature modern interlayer potentials, and a
modification of the hopping parameters between layers in the light of the
classic Slonczewski-Weiss-McClure parametrisation. We shall show that flat
bands result in all cases, but that their nature can be rather different. We
will show how to construct a more general reduction to a continuum model, and
show that even though such a model can be constructed, its complexity
increases, requiring more coupling parameters to be included, and the full
in-layer dispersion to be taken into account. We conclude that the combination
of all these effects will have a large impact on the wave functions of the flat
bands, and that changes in the detail of the underlying models can lead to
significant changes. A robust conclusion is that the natural strength of the
interlayer couplings is higher than usually assumed, which causes additional
Dirac points to appear for the standard magic angles. This gives rise to a
degeneracy at the $\Gamma$ point. Since the appearance of a gap at the $\Gamma$
point is crucial for the construction of the Wannier states which are used in
the standard descriptions of superconductivity, such an approach not be robust.
