Behaviour of R_I, ±  (σ₊ + σ₋, left panels), and R_I, + 0 (σ₊ + π₀, right panels). Top panels: the resulting blend depth when both components have equal depth (abscissa values) for different angles γ ranging from π/4 to π/2 (top to bottom solid lines). The dashed line represents the linear sum of the two components. Middle panels: component depth for which the relative error with respect to the linear approximation δR_I/R_I is largest, depending on the angle γ. Lower panels: maximum relative errors δR_I/R_I as a function of γ. See text for detailed discussion.