Left panel: limits for the presence of a BLR from Elitzur & Shlosman (2006), Laor (2003), and Nicastro (2000). These models predict that objects located in the portion of the plane below the dashed lines cannot form a BLR. Left panel: predictions on the transition radius between the geometrically thick and thin regions of the accretion disk in a pure ADAF model and Evaporation model (models A and C from Czerny et al. 2004, adopting α = 0.1 and β = 0.99, see text).