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.

7 pages, 3 figures. MNRAS in press