Top: |Δτ| (Eq. (9)) versus A_V (left) and τ_int ≡ ∫ τdv (right) for the central+off-axis subset, with the horizontal dashed line showing the median value. Note that A_V and τ_int are measured toward pointing centers. Also shown are median and maximum of |Δτ| per pointing, and median |Δτ| in equal frequency bins. The 1σ uncertainty on averaged |Δτ| per bin is too small and not shown. For clarity, one measurement with |Δτ| = 2.53 is omitted from the plot. Bottom: |Δτ_rel| (Eq. (10)) versus A_V (left) and τ_int ≡ ∫ τdv (right). For clarity, one measurement with |Δτ_rel| = 1.66 is omitted from the plot. The remaining details are same as top panels.