On the driver of relativistic effect strength in Seyfert galaxies M. Guainazzi, S. Bianchi, I. de la Calle Pérez, M. Dovčiak and A. L. Longinotti A&A, 531 (2011) A131 Published online: 30 June 2011 DOI: 10.1051/0004-6361/201016245