  A number of studies have shown that the visibility of scattered broad
emission lines in Seyfert 2 galaxies is strongly dependent on the IRAS
f_60/f_25 flux ratio, where those Seyfert 2s with `warm' IRAS colours show
polarised broad line emission. It is now clear that this effect is due to the
increasing dominance of the galactic rather than the AGN emission at 60um in
less luminous `cool' Seyfert 2s. However, we present evidence that the 25um
emission is a good measure of the AGN luminosity for most Seyfert 2s. Using
this result, we show that the visibility of scattered broad line emission has a
dependence on the AGN luminosity. The observations can be interpreted
self-consistently if the scale height of the scattering zone varies with
central source luminosity whilst the scale height of the obscuring torus is
approximately constant.
