  Dabconium hybrid perovskites include a number of recently-discovered
ferroelectric phases with large spontaneous polarisations. The origin of
ferroelectric response has been rationalised in general terms in the context of
hydrogen bonding, covalency, and strain coupling. Here we use a combination of
simple theory, Monte Carlo simulations, and density functional theory
calculations to assess the ability of these microscopic ingredients---together
with the always-present through-space dipolar coupling---to account for the
emergence of polarisation in these particular systems whilst not in other
hybrid perovskites. Our key result is that the combination of A-site polarity,
preferred orientation along $\langle111\rangle$ directions, and ferroelastic
strain coupling drives precisely the ferroelectric transition observed
experimentally. We rationalise the absence of polarisation in many hybrid
perovskites, and arrive at a set of design rules for generating FE examples
beyond the dabconium family alone.
