Posterior distributions of BLR radius (left column) and BH mass (right column) resulting from BLR fitting without differential phase data (blue histogram) and with differential phase data (orange histogram). Each row corresponds to each target; from top to bottom: Mrk 509, PDS 456, Mrk 1239, and IC 4329A. The histograms are normalised such that they integrate into 1. It is clear that the spatial information from the differential phase significantly constrains both the BLR radius and BH mass.