  The optical Fundamental Plane of black hole activity relates radio continuum
luminosity of Active Galactic Nuclei to [O III] luminosity and black hole mass.
We examine the environments of low redshift ($z<0.2$) radio-selected AGN,
quantified through galaxy clustering, and find that halo mass provides similar
mass scalings to black hole mass in the Fundamental Plane relations. AGN
properties are strongly environment-dependent: massive haloes are more likely
to host radiatively inefficient (low-excitation) radio AGN, as well as a higher
fraction of radio luminous, extended sources. These AGN populations have
different radio -- optical luminosity scaling relations, and the observed mass
scalings in the parent AGN sample are built up by combining populations
preferentially residing in different environments. Accounting for
environment-driven selection effects, the optical Fundamental Plane of
supermassive black holes is likely to be mass-independent, as predicted by
models.
