Ratio between galaxy-scale and sub-pc-scale outflow momentum rates for different QSOs hosting UFOs. Measurements for individual galaxies are shown as squares (ionised outflows), circles (molecular outflows), and diamonds (atomic outflows) with error-bars. Systems are ordered by increasing L_BOL. The horizontal dashed line shows the prediction for momentum-driven winds (ṗ_out/ṗ_UFO = 1), individual predictions for energy-driven winds are shown as orange rectangles. Our Hα and [O III] measurements for MR 2251−178 and PG 1126−041 are shown separately using filled and empty symbols, respectively.