  Empirical models of galaxy formation require assumptions about the
correlations between galaxy and halo properties. These may be calibrated
against observations or inferred from physical models such as hydrodynamical
simulations. In this Letter, we use the EAGLE simulation to investigate the
correlation of galaxy size with halo properties. We motivate this analysis by
noting that the common assumption of angular momentum partition between baryons
and dark matter in rotationally supported galaxies overpredicts both the spread
in the stellar mass-size relation and the anticorrelation of size and velocity
residuals, indicating a problem with the galaxy-halo connection it implies. We
find the EAGLE galaxy population to perform significantly better on both
statistics, and trace this success to the weakness of the correlations of
galaxy size with halo mass, concentration and spin at fixed stellar mass. Using
these correlations in empirical models will enable fine-grained aspects of
galaxy scalings to be matched.
